1485740_Dinoflagellate Cyst Taxonomy and Biostratigraphy of the Eocene Bracklesham Group InSouthern...

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Dinoflagellate Cyst Taxonomy and Biostratigraphy of the Eocene Bracklesham Group inSouthern EnglandAuthor(s): M. A. IslamReviewed work(s):Source: Micropaleontology, Vol. 29, No. 3 (1983), pp. 328-353Published by: The Micropaleontology Project, Inc.Stable URL: http://www.jstor.org/stable/1485740 .Accessed: 23/10/2012 01:35

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Dinoflagellate cyst taxonomy and biostratigraphy of the Eocene Bracklesham Group in southern England

ABSTRACT

Dinoflagellate cysts are documented from the Bracklesham Group of Eocene age at Bracklesham Bay, southern England. Stratigraphically significant species permit subdivision of the section into three of the assemblage zones of Bujak et al. (1980b): Pentadinium laticinctum Assemblage Zone (B-2), Phthanoperidinium comatum Assemblage Zone (B-3), and Areosphaeridium arcuatum Assemblage Zone (B-4), in ascending order. The studied section at Bracklesham Bay is biostratigraphically correlated with sections at Whitecliff Bay and Alum Bay previously studied by Eaton (1976). The three formations, Wittering, Earnley and Selsey, belonging to the Bracklesham Group are delimited at Alum Bay, and a possibility of redefining the top of the Group is discussed. This correlation indicates that the lithostratigraphic boundaries are almost synchronous. Selected taxa, including mostly new and reattributed taxa, are dealt with in the Systematics section herein, which includes one new genus, Trivalvadinium, and 18 new species. Four species/subspecies are generically reattributed and diagnoses of two reattributed taxa are emended. One subspecies is raised to specific level.

INTRODUCTION

The Bracklesham Group is recognized only in the Hampshire Basin, southern England. Historically, most English Eocene formations although rich in fossils have not proved significantly useful for biostratigraphic studies until very recently, but the Bracklesham Group with its Nummulites beds has always been one of the exceptions and important for biostratigraphic considerations. Other fossils in the Brack- lesham Group, although abundant and diverse, were less useful than the Nummulites in biostratigraphic studies. Therefore, in the absence of the Nummulites beds in particular, it has been difficult to recognize and delimit the Group in near-shore paleoenvironments.

Eaton (1971a, 1971b, 1976) studied dinoflagellate cysts from the Bracklesham Group in the Isle of Wight. He demonstrated their use- fulness in resolving the problems of correlation of the Eocene in southern England, but many historical problems of stratigraphic nomenclature, correlation, and related matters have not yet been adequately solved. This paper deals with certain of these problems that relate to the Brackle- sham Group in the Hampshire Basin. The Group's relationship to the succession in the London Basin will be dealt with in a subsequent paper.

Twenty-two samples were obtained from the middle of the Wittering Formation through the Earnley Formation to the lower part of Selsey Formation of the Bracklesham Group at Bracklesham Bay, which lies between Chichester Harbour and Selsey Bill (text-fig. 1). The outcrops occur discontinuously on the foreshore, frequently blanketed by tidal sands and clays, and are best observed at low spring tides. The se- quence is never completely exposed at any one time, and some parts of the section have never been accessible.

Organic residues were concentrated by applying standard acid macer- ation techniques: carbonates removed by dilute hydrochloric acid, sil- icates by dilute hydrofluoric acid, and residual mineral grains and larger organic debris by swirling in a large watch glass.

Reference and type materials have been stored at the Micropalaeon- tology Laboratory of the Department of Geology, University of Shef- field, United Kingdom. Slide reference numbers have been given in the text and in the captions to plates. Specimen locations on the slides follow the slide number and are in England Finder co-ordinates. Specimen dimensions given as A x B are length x breadth, excluding processes; the figure in parenthesis is the average and is flanked by the figures of largest and smallest dimensions. Occurrence indicates the first and last occurrences; peak occurrence is the percentage of

micropaleontology, vol. 29, no. 3, pp. 328-353, pls. 1-4, 1983

M. A. Islam 9/28 The Avenue Nedlands Western Australia 6009

328

Micropaleontology, vol. 29, no. 3, 1983

TEXT-FIGURE 1 Map of part of southern England showing studied localities and extent of Tertiary Hampshire Basin.

total dinoflagellates and acritarchs based on 200 counts (not given when under 3%). Locations of other occurrences are: Baughurst, Shapley Heath, Chobham Common, and Virginia Water in the western London Basin, Sheppey in the eastern London Basin, and Egem in western Belgium.

STRATIGRAPHY

The Bracklesham Group of middle Early Eocene to late Middle Eocene age overlies the Whitecliff Member of the London Clay Formation or the London Clay proper where that member is not recognized. It consists of sands, silts and clays, mainly of marine origin in the eastern Hampshire Basin that contains Nummulites beds and glauconitic sands. The sediment source lies in the west, and increasingly nonmarine sediments are encountered progressively toward the west (Reid 1899). The lower contact of the Group with the London Clay is conformable but frequently characterized by a basal pebble bed (King 1981). The upper contact with the Barton Formation as it is presently defined (Cooper 1976) is conformable, but with the top of the Group redefined as recommended in the present paper, it would be erosional and unconformable.

In a comprehensive study of the Group, Fisher (1862) described the Bracklesham Beds (Formation) with the stratotype at Whitecliff Bay, eastern Isle of Wight. He classified the stratotype into 19 beds (I to XIX in ascending order). These beds still form a useful standard reference. Prestwich's (1846) numerically designated beds are also a helpful reference. Fisher's (1862) Bracklesham Beds essentially correspond to Prest- wich's (1847) Bracklesham Bay Series with a slightly lowered top. Eaton (1971a, 1976) further lowered the top slightly (within Fisher bed XIX). The Bracklesham Group encompasses Prestwich's beds 6 through part of 17 at Whitecliff Bay and beds 8 through part of 29 at Alum Bay.

Curry et al. (1977) presented a detailed account of the Group from the foreshore exposures at Bracklesham Bay. They recognized three sedimentary cycles in the Group and informally designated them as Wittering, Earnley, and Selsey divisions, in ascending order. The Wittering division was further classified into 17 beds, W1 to W17, the Earnley division into 12 beds, E1 to E12, and the Selsey division into 11 beds, S1 to S11, all in ascending orders. Stinton (1975) had already awarded the status of formal formations to the infor-

329

M. A. Islam: Dinoflagellate cyst taxonomy and biostratigraphy of the Eocene Bracklesham Group in southern England

mal divisions under the Bracklesham Group. He said nothing about the stratotypes of these formations, which were rightly stated by Curry et al. (1977) to be at Whitecliff Bay, the stratotype of the Bracklesham Beds of Fisher (1862); therefore, Cooper's (1976) references to East Wittering and Selsey as stratotype localities of the Wittering and Selsey Formations, respectively, and attribution of these assignations to Stinton are erroneous.

Stinton's action of awarding formational status to what were proposed to be informal "divisions" has been disputed by King and King (1977), who divided the Earnley "division" (Formation) into Earnley and Marsh Farm Formations without defining the status of the Earnley Formation of Stinton (referred to in this paper). The Wittering "division" (Formation) was also further subdivided into three formations (King and Kemp 1982). These actions do not appear to be in accord with rec- ommendations made in various stratigraphic codes and are likely to add to legal and nomenclatural complica- tions.

There are apparently differences of opinion about the upper part of the Group. Curry et al. (1977) recognized an upper Huntingbridge division comprising Fisher beds XVIII and XIX at Whitecliff Bay, which is absent from the Bracklesham Bay. Stinton (1975), while formalizing it as a formation within the Bracklesham Group, as- signed only Fisher bed XIX to this formation. Cooper (1976) relegated it to a member of the Selsey For- mation which appears to have been ignored by Curry et al. (1978). However, the Huntingbridge division is treated as a member of the Selsey Formation in this paper mainly because it does not, like other formations of the Group, represent a complete sedimentary cycle. This matter is further discussed later.

Fisher (1862) recorded Nummulites laevigatus (Bru- guiere) in bed VII and N. variolarius (Lamarck) in bed XVII. Wrigley and Davis (1937) discovered N. planulatus (Lamarck) in Fisher bed IV. These species were used as evidence for attributing the European stage names Cuisian, Lutetian, and Auversian to the Brack- lesham Group. This practice has now been discontin- ued, owing to the confusion surrounding the concept of these stages in Europe (Curry 1965). Nevertheless, the stage names are often used in informal references to relative biostratigraphic positions.

The Nummulites beds have been used to advantage in correlating the Group with neighboring and conti- nental successions. But the absence of most of these beds at Alum Bay, western Isle of Wight, has led to confusing lithostratigraphic designations and delimi- tations by all workers (e.g. Bristow 1862, Gardner 1879, White 1921) after Prestwich (1847). Subsequently, Ea- ton (1971a) delimited the Bracklesham Group (Beds)

on dinoflagellate evidence. He formally defined five Microplankton Zones in the Group numbered 1 to 5 in ascending order (Eaton 1976). Bases of Zones 2 and 4 coincided with first occurrences of Nummulites planulatus and N. laevigatus, respectively. These zones have since been redefined as assemblage zones with type sections at Whitecliff Bay, given names after an important species occurring in each zone and renum- bered B-1 to B-5 (Bujak et al. 1980b).

The top of the Bracklesham Group has been defined just below the first occurrence of Nummulites prestwichianus (T. R. Jones) (Cooper 1976). Dinoflagellate evidence has also been used to support this course in the western part of the Hampshire Basin (Costa et al. 1976). DINOFLAGELLATE BIOSTRATIGRAPHY

Assemblage zones

The sampled section of the Bracklesham Group at Bracklesham Bay is classified into the following dinoflagellate assemblage zones defined in Bujak et al. (1980b) by first and last occurrences of selected species that are considered stratigraphically significant. First occurrences of species were found more consistent in the present study and also by Costa and Downie (1976) and therefore more reliable in defining the zones. A zone has been recognized in a stratigraphic interval in which the definitive zone-species first and last occurred. In the present study, the lower boundary of a zone has been arbitrarily made to coincide with a lithological boundary, for convenience. Possible error is expected to be inconsequential due to close sampling of the section. The upper boundary has been placed to coincide with the base of the next higher zone mainly owing to probable reworking of some of the definitive last-occurring zone-species (text- fig. 2). Pentadinium laticinctum Assemblage Zone (B-2)

This zone includes lithologic units W10 through W15 and is characterized by first occurrences of the following species: P. laticinctum Gerlach 1961 and Turbio- sphaera galatea Eaton 1976 in lithologic unit W10; Gla- phyrocysta laciniiforme (Gerlach) Stover and Evitt 1978 in unit W11; and G. spineta (Eaton) Stover and Evitt 1978 and Hystrichokolpoma salacium Eaton 1976 in unit W13. Other species found to first appear in this zone and considered stratigraphically significant are: Cleistosphaeridium spinulastrum Islam, n. sp., Hystri- chokolpoma manipulatum Islam 1983 and Selenopem- phix nephroides Benedek 1972 in unit W11; and Ar- eosphaeridium sp. A in unit W14.

The last occurrence of two species in this zone has been recorded by Bujak et al. 1980b: Adnatosphaeri- dium robustum (Morgenroth) De Coninck 1976 in unit W13, whose reappearance high in the section is prob-

330

Hystrichosphoeridium solpingophorum Impletosphoeridium Implicotum Glaphyrocysta reticulosa G. divaricata G. ordinota Deflandrea denticulato Cordosphaeridlum fibrospinosum Homotryblium sp. A H.tubiferum brevispinum Areoligero coronato Wetzeliella somlandica Klsselovia tenuivirgulo Areoligero cf. senonensis A. cf. coronoto A. senonensis Adnatosphaerldlum robustum Wetzellello meckelfeldensls Lonternosphoerldlum lonosum

Apectodinlum folliculum n. sp. Operculodi nium crassum Trivolvadinium formosum n.gen,n.sp. Fibrocysta radlata Homotryblium abbrevlatum

Dinopteryglum cladoides Lejeunia hyalina Hystrichokolpoma granulatum Pentodinium laticinctum Turbiosphaera galatea Glaphyrocysta locinilforme

Selenopemphix nephroldes Cleistosphaerldlum spinulastrum n. sp.

Hystrichokolpoma manipulum Glophyrocysto spineta Hystrichokolpoma salocium Impletosphaerldium kroemmelbelnll

Phthonoperldlnlum comotum

Impletosphaeridlum luxurlum

Areosphaeridium diktyoplokus Impletosphaeridlum cracens ?Alterbia earnleyense n.sp. Diphyes ficusoides n sp. Thalossiphora decrementa n.sp Wetzellella hoampdenensis Ar e o I g era sentosa A. touloma Deflandrea translucida Homotryblium caliculum

Polysphaeridium biformum n.sp. Cordosphaerldium contherellum Homotryblium oceanicum Araneosphaera oraneoso

Homotryblilum deconinckil n.sp. Turbiosphaera mognlfica Areosphaeridium arcuatum Distotodinium ellipticum Ascostomocystis laoevigatus Operculodinlum exqulsitum n. sp.

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Phthanoperidinium comatum Assemblage Zone (B-3)

This zone includes lithologic units W16 through E4 and is recognized by first occurrences of the following species: P. comatum (Morgenroth) Eisenack and Kjell- str6m 1971 and Impletosphaeridium luxurium Eaton 1976 in lithologic unit W16; Areosphaeridium diktyoplokus (Klumpp) Eaton 1971 b and Impletosphaeridium cracens Eaton 1976 in unit W17; and Areoligera sentosa Eaton 1976 and Areoligera tauloma Eaton 1976 in unit E2. Other species first appearing in this zone and considered stratigraphically significant are: ?Alter- bia earnleyense Islam, n. sp., Diphyes ficusoides Is- lam, n. sp., Thalassiphora decrementa Islam, n. sp. and Wetzeliella hampdenensis Wilson 1967 in unit E1; De- flandrea translucida Chateauneuf 1980 in unit E2; and Homotryblium caliculum Bujak 1980 in unit E3.

Among the last occurring species in the zone (Bujak et al. 1980b) are: Turbiosphaera galatea Eaton 1976 in unit E4 and Wetzeliella meckelfeldensis Gocht 1969 above the zone sporadically, probably due to reworking; but Hystrichokolpoma granulatum Eaton 1976 continues to occur regularly above this zone.

Areosphaeridium arcuatum Assemblage Zone (B-4)

This zone includes lithologic units E5 through S3 and is recognized by first occurrences of the following: Homotryblium oceanicum Eaton 1976 in lithologic unit E5; and Turbiosphaera magnifica Eaton 1976 and A. arcuatum Eaton 1971b in unit E8. Homotryblium deconinckii Islam, n. sp. occurring in unit E6 is also considered stratigraphically significant.

Among last occurring species, Areoligera cf. coronata (O. Wetzel) Lejeune-Carpentier 1938 sensu Williams and Downie 1966b last occurs in unit W16; Areoligera cf. senonensis Lejeune-Carpentier 1938 sensu Wil- liams and Downie 1966b in unit E8; Chiropteridium cf. dispersum Gocht 1960 sensu Eaton 1976 in unit E6; Cordosphaeridium fibrospinosum Davey and Williams 1966 and Kisselovia tenuivirgula (Williams and Down- ie) Lentin and Williams 1976 in unit S2; and Glaphy- rocysta divaricata (Williams and Downie) Stover and Evitt 1978, Glaphyrocysta ordinata (Williams and Downie) Stover and Evitt 1978 and Impletosphaeri- dium implicatum Morgenroth 1966 in unit S3, the high- est sampled unit. The top of the zone remains unde- termined.

Correlation

The Bracklesham Group at Bracklesham Bay and Whitecliff Bay was thought to be correlative almost bed for bed (Curry 1965) and was correlated as such by Curry et al. (1977). Correlations based on dinoflagellates shown in text-figure 3, are believed to be more

precise. The lignite bed at Whitecliff Bay immediately underlying Zone B-3 is correlated herein on dinoflagellate evidence with the coarse- to medium-grained "very lignitic sands" (unit W15) underlying the same zone at Bracklesham Bay. Coincidence of the base of Zone B-4 at both places with the first occurrences of Nummulites laevigatus is also significant.

Curry et al. (1977) traced the boundaries of the Wit- tering, Earnley, and Selsey formations to Whitecliff Bay. They are traced further west at Alum Bay as follows (text-fig. 4):

Selsey Formation - Prestwich (1846) beds 25-29(part) = Eaton (1971a, 1976) beds 15-19.

Earnley Formation - Prestwich beds 15(part)-24 = Eaton beds 4-15.

Wittering Formation - Prestwich beds 8-15(part) = Eaton beds 1-3.

The Huntingbridge Member of the Selsey Formation constitutes Prestwich bed 29(part) = Eaton bed 19 only.

The tops of the Wittering and Earnley formations and that of the Selsey Formation minus the Huntingbridge Member are eroded surfaces overlain by pebble beds, implying erosion in basin marginal areas upon termination of each sedimentary cycle. These lithostratigraphic boundaries, when compared with Eaton's (1971a, 1976) correlations appear to be almost synchronous, if the apparent diachronisms are explained by erosion at Alum Bay (text-fig. 4). Further west, the Bracklesham Group is not recognizable due to pre- dominance of nonmarine sediments. However, Costa et al. (1976) correlated the upper part of the Bourne- mouth Marine Beds, Boscombe Sands and Hengist- bury Beds below the Nummulites prestwichianus bed in Bournemouth and neighboring area with the young- est Bracklesham Group, on dinoflagellate evidence.

TOP OF BRACKLESHAM GROUP: A DISCUSSION

The top of the Bracklesham Group as it is presently defined coincides with a biostratigraphic datum underlying the Nummulites prestwichianus bed. Apart from the legality of the matter (a group is a lithostratigraphic unit and should be bounded by lithostratigraphic planes), this is inconsistent with the nature of the other boundaries of its constituent formations, which are lithostratigraphically defined. It appears to be more appropriate that the top of the Bracklesham Group be defined at an important geological event. Such an event is the termination of the Selsey cycle, defined at the tops of the Prestwich bed 28 and Eaton bed 18 at Alum Bay, and Fisher bed XVII at Whitecliff Bay (text-fig. 4). This is a well-recognized lithostratigraphic boundary with eroded surfaces overlain by pebble beds from Afton westwards (cf. fig. 3 of Costa et al. 1976, cf. Murray and Wright 1974) and coincides with the top of the Boscombe Sands and the bottom

332


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Lithostratigraphic boundary Microplankton Assemblage Zone boundary _- - Correlation of Curry et al., 1977

TEXT-FIGURE 3 Palynostratigraphic correlation of the Bracklesham Group at Bracklesham Bay with the stratotype of the Group at Whitecliff Bay. This is

compared with the last previous correlation by Curry et al. 1977, from whom the occurrences of larger foraminifera are taken.

333

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Alum Bay 262 m.

Whitecliff Bay 197 m.

Bracklesham Bay 122m.

TEXT-FIGURE 4 Lithostratigraphic boundaries, particularly tops of Wittering and Earnley formations and that of the Selsey Formation minus Huntingbridge Member are almost synchronous. Apparent diachronism is probably adequately compensated by erosions at these levels at Alum Bay.

of the Hengistbury Beds in the Bournemouth area. As with other lithostratigraphic boundaries, this extended surface also appears synchronous with slight diachronism possible. To redefine the top of the Brackle- sham Group at this level, it would be necessary to reattribute the Huntingbridge Member to the overlying Barton Formation. Redefinition of the top of the Brack-

lesham Group as suggested will not affect the Lute- tian/Bartonian or Middle/Late Eocene boundary taken at the base of the N. prestwichianus bed.

SYSTEMATICS

Division PYRRHOPHYTA Pascher Class DINOPHYCEAE Fritsch Order PERIDINIALES Haeckel

334


Achilleodinium Eaton 1976

Type species: Achilleodinium biformoides (Eisenack) Eaton 1976.

Achilleodinium fibrapendiculum Islam, n. sp. Plate 1, figures 1-3; text-figure 5

Cordosphaeridium fibrospinosum Davey and Williams.-EATON 1976, pl. 6, fig. 6. Eocene.

Derivation of name: Latin: fibra = filament, thread; appendicis = appendage; -ulus = diminutive; refers to its fibrous processes.

Diagnosis: Cyst ellipsoidal, skolochorate and biphragmal; periphragm fibrous/fibroreticulate; intratabular fibrous processes proximally closed and distally entirely open or closed; epi- and hypocystal processes broad, with more or less equidimensional cross sections, but paracingular processes broad, parallel to paracingulum but very narrow perpendicular to it; anterior processes generally smaller in all dimensions than posterior ones; antapical process sometimes longest and broadest of all, possessing a few lateral spines distally and frequently a closed domal tip; one process per paraplate defining a paratabulation of 4', 6", 4-6c, 5"', 1 p, 1"", xs; paracingulum slightly helicoidal; parasulcus sometimes very narrow, straight, extending over both cyst halves; archeopyle precingular type P, representing paraplate 3", operculum free.

Types: Holotype: Slide BB-31(3),L40.4; Bed S3, Sel- sey Formation, Middle Eocene. Paratype: Slide BB- 30(3),V47.2.

Dimensions: Holotype: cyst body 52 x 47 um; length of processes 11-15 ,/m, breadth 8-15 A/m. Range: cyst length 68(54)46 /m, breadth 57(48)44 /m, length and breadth of processes 8-15 ,/m. Specimens measured: 13.

Occurrence: BB-30-BB-31, peak BB-30, 22%. Other occurrence: Sheppey.

Remarks: This species differs from others of the genus in possessing fibrous processes. It resembles Cordosphaeridium fibrospinosum but differs in possessing narrower paracingular processes and smaller cyst and process dimensions. Cordosphaeridium fibrospinosum is roughly a fourth to twice larger and possesses about twice longer processes, showing no size differentiation between anterior and posterior processes.

Alterbia Lentin and Williams 1976

Type species: Alterbia recticornis Vozzhennikova ex Stover and Evitt 1978.

view

\j , Ventral view

TEXT-FIGURE 5 Achilleodinium fibrapendiculum Islam, n. sp. Camera lucida sketch of the holotype.

?Alterbia bicellula Islam, n. sp. Plate 1, figures 6-7

Derivation of name: Latin: bi = two, double; cella = chamber; -ulus = diminutive; refers to its bicavate cysts.

335


Diagnosis: Pericyst dorsoventrally compressed peridinioid with short, conical apical horn commonly having rounded tip, broadening proximally to merge to epipericyst ambitus, and two unequal antapical horns, the left broad-based and conical with pointed tip and more or less equal in length to the apical horn, the right reduced, with a rounded tip; endocyst subspherical and oblate; proximate and bicavate; both phragma thin, chagrinate and sometimes wrinkled; folds in periphragm always defining paracingulum, which may be slightly helicoidal and sunken; parasulcus sometimes indicated by slight depression; archeopyle intercalary type I/I with standard hexa style, operculum attached; epipericoel with or without communication to exterior.

Types: Holotype: Slide BB-29(1),C42.4; Bed E11, Earnley Formation, Middle Eocene. Paratype: Slide BB- 29(2),V49.4.

Dimensions: Holotype: pericyst 54 x 47 ,/m, endocyst 36 x 46 Am, archeopyle index 0.49. Range: pericyst length 60(54)48 gm, breadth 54(49)43 ,/m; endocyst length 45(39)31 /um, breadth 53(47)42 /,m; archeopyle index 0.60(0.53)0.49 (9 specimens). Spec- imens measured: 13.

Occurrence: BB-18-BB-29, peak BB-29, 8%. Other occurrences: Baughurst, Shapley Heath, Virginia Water, Sheppey, Egem.

Remarks: The generic assignment of the species is based on general morphology, but questioned because the epipericoel is not always communicative to the exterior, and its degree of cavation and the archeopyle index do not match those prescribed for the genus. The degree of cavation and the archeopyle index of this species also do not match those of other peridinioid genera that are differentiated on the basis of these features by Lentin and Williams (1976). These features serve to differentiate it from other species of the genus.

The problem was discussed by Stover and Evitt (1978) who met with "greatest difficulties" in drawing generic limits of their Peridiniacean genera of Subcate- gory 3D which includes Alterbia. They also noted that species attributed to the genera of this subcategory "exhibit shades of difference and degree of morpho- logic overlap that leave many uncertainities about what criteria should be applied." In view of these difficulties, tentative allocation of the species to Alterbia is pre- ferred to creating a new genus to accommodate it.

?Alterbia earnleyense Islam, n. sp. Plate 1, figures 10-11

Derivation of name: After Earnley, a township neighboring the foreshore exposures of the Earnley For- mation at Bracklesham Bay.

Diagnosis: Pericyst dorsoventrally compressed peridinioid with short, conical apical horn having pointed or rounded tip, broadening proximally to merge with epipericyst ambitus, and only left antapical horn which is similarly conical, broad-based and equally long with pointed or rounded tip; right antapical horn, if present, vestigial; endocyst oblate and subspherical; both phragma thin and chagrinate, sometimes wrinkled; proximate and cornucavate to narrowly bicavate; folding in periphragm always defining paracingulum, which is slightly helicoidal and sometimes sunken; parasulcus sometimes indicated by slight depression; archeopyle intercalary type I/I with standard hexa style, operculum attached or free; epipericoel may or may not be in communication to exterior.

Types: Holotype: Slide BB-29(1),M47.4; Bed E11, Earnley Formation, Middle Eocene. Paratype: Slide BB- 28(1),030.4.

Dimensions: Holotype: pericyst 54 x 44 Am, endocyst 37 x 43 gm, archeopyle index 0.51. Range: pericyst length 58(53)49 ,/m, breadth 52(48)44 /tm; endocyst length 48(39)31 ,um, breadth 51(47)43 ,m; archeopyle index 0.59(0.52)0.49 (5 specimens). Spec- imens measured: 11.

Occurrence: BB-19-BB-30, peak BB-29, 12%. Other occurrence: Shapley Heath.

Remarks: The remarks made on the generic assignment of ?A. bicellula, n. sp. are also relevant to this species. The holotype of ?A. earnleyense, n. sp. (pl. 1, fig. 10) vaguely indicates the presence of accessory sutures adjacent to the archeopyle, implying possible involvement of other adjacent paraplates in archeopyle formation. But this could not be conclusively deter- mined, as most of the specimens did not indicate an archeopyle.

?Alterbia earnleyense, n. sp. differs from ?A. bicellula, n. sp. in possessing one antapical horn. This distinction may possibly be argued to be infraspecific, but the two species are distinguished because of their relative stratigraphic significance. ?Alterbia earnleyense, n. sp. is stratigraphically younger.

Apectodinium (Costa and Downie) Lentin and Williams 1977

Type species: Apectodinium homomorphum (De- flandre and Cookson) Lentin and Williams 1977.

Apectodinium folliculum Islam, n. sp. Plate 1, figures 8-9

Derivation of name: Latin: folliculus = inflated ball; refers to the cyst ambitus.

Diagnosis: Cyst ambitus subcircular to elliptical or roundly pentagonal without horns or with very minor

336


ones; acavate to slightly cornucavate; proximochorate; periphragm mildly chagrinate; many, sometimes fewer, nontabular processes thin, solid and thinly tubular, slender to somewhat flexible, distally aculeate and open when hollow, proximally wide and sometimes joining in groups; paracingulum generally not indicated; archeopyle intercalary type I/I but generally indistinguishable, its absence in subspherical forms, making orientation difficult.

Types: Holotype: Slide BB-27(1),P42.1; Bed E10, Earnley Formation, Middle Eocene. Paratype: Slide BB- 12(1),M42.2.

Dimensions: Holotype: cyst body 54 x 56 /m, length of processes 5-8 /um. Range: cyst length 68(53)42 /,m, breadth 62(52)42 ,im, length of processes 3-13 /im. Specimens measured: 10.

Occurrence: BB-10-BB-30, peak BB-27, 40%. Other occurrences: Baughurst, Shapley Heath, Chobham Common, Virginia Water.

Remarks: This species differs from others of the genus in possessing a roundish cyst with vestigial horns or, generally, being without horns. In process morphology it resembles Apectodinium summissum Har- land 1980 and Trivalvadinium formosum Islam, n. gen., n. sp. and may be related to both species. The former species differs in possessing two antapical horns, the latter in possessing a 31 archeopyle.

Areosphaeridium Eaton 1971 a

Type species: Areosphaeridium diktyoplokus (Klumpp) Eaton 1971 a.

Areosphaeridium sp. A. Plate 1, figure 5

Description: Autophragm chagrinate, granulate or reticulate; many intratabular processes with 3 to 4 per paraplate, solid and somewhat fibrous, 1 to 2 /m thick in stems and a quarter to under half cyst diameter in length, distally ramified in membranous palmate expansions with indented margins; archeopyle apical type tA.

Cleistosphaeridium Davey, Downie, Sarjeant and Williams 1966

Type species: Cleistosphaeridium diversispinosum Davey, Downie, Sarjeant and Williams 1966.

Cleistosphaeridium selseyense Islam, n. sp. Plate 2, figures 3, 7

Cleistosphaeridium sp. A JAIN and TANDON 1981, p. 8, pi. 4, fig. 61.

Derivation of name: After Selsey, a township neighboring the foreshore exposures of the Selsey Forma- tion at Bracklesham Bay.

Diagnosis: Autocyst subspherical; surface mildly reticulate; skolochorate to proximochorate; numerous nontabular solid processes a third to a quarter of average cyst diameter in length, proximally wide and taeniate and sometimes joined proximally to adjacent ones, tapering rapidly to thin, slender forms at or below mid-length and continue as such to distal bifur- cations; archeopyle apical type tA, operculum free or attached. In some forms, a thin psilate proximal mem- brane connects most processes, a feature found in some species of Impletosphaeridium Morgenroth 1966 (Islam 1983).

Types: Holotype: Slide BB-31(2),S38.4; Bed S3, Sel- sey Formation, Middle Eocene. Paratype: Slide BB- 31(1),L37.3.

Dimensions: Holotype: cyst diameter 30 /im, length of processes 4-7 ,im. Range: cyst diameter 31(26)22 g/m, length of processes 3-8 /im. Specimens measured: 10.

Occurrence: BB-10-BB-31, peak BB-31, 17%. Other occurrences: Baughurst, Virginia Water, Sheppey, Egem.

Remarks: This species differs from others of the genus in possessing proximally taeniate and distally thin solid processes, and smaller size.

Cleistosphaeridium spinulastrum Islam, n. sp. Plate 2, figures 1-2

Derivation of name: Latin: spinula = thorn; -astrum = suffix implying likeness; refers to its morphological likeness to Diphyes spinula (Drugg) Stover and Evitt 1978.

Diagnosis: Cyst subspherical and skolochorate with chagrinate surface; numerous nontabular, elongate conical processes of more or less half cyst diameter in length, hollow, closed at both ends, tapering from broad circular bases to narrow solid necks and acuminate, entire or rimmed distal tips; pairs of processes frequently proximally joined; paracingulum not indicated; archeopyle apical type tA.

Types: Holotype: Slide BB-24(2),T35.2; Bed E6, Earn- ley Formation, Middle Eocene. Paratype: Slide BB- 24(1),K46.4.

Dimensions: Holotype: cyst body 28 x 38 /um (without operculum), length of processes 10-13 /m. Range: cyst length 33(28)23 gm, breadth 38(31)26 g/m, length of processes 10-17 gm. Specimens measured: 7.

Occurrences: BB-1 1-BB-31. Other occurrences: Sheppey, Egem.

Remarks: This species differs from others of the genus in process morphology by which it resembles Di-

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phyes spinula but differs in lacking the distinctively broad antapical process. It also resembles Dapsilidi- nium pastielsii (Davey and Williams) Bujak et al. 1980c but differs in possessing distally closed processes. However, C. spinulastrum n. sp. and D. pastielsii are morphogenetically related through transitional forms, but the former could not be referred to Dapsilidinium Bujak et al. 1980c, as the genus is characterized by distally open processes while the generic circumscrip- tions of Cleistosphaeridium readily accommodated the species. Cleistosphaeridium spinulastrum, n. sp. is also stratigraphically significant and younger.

Cordosphaeridium Eisenack 1963, emend. Davey 1969

Type species: Cordosphaeridium inodes (Klumpp) Ei- senack 1963, emend. Morgenroth 1968.

Cordosphaeridium minus (Morgenroth) Islam, n. status Plate 1, figure 4

Cordosphaeridium inodes subsp. minus MORGENROTH 1966, p. 24, pl. 5, figs. 4-5. Early Eocene.

Remarks: The status of the taxon is raised in view of its dubious relations with the type, as some forms of the taxon show transitions to Cordosphaeridium exi- limurum Davey and Williams 1966.

Danea Morgenroth 1968, emend. Drugg 1970

Type species: Danea mutabilis Morgenroth 1968.

Danea impages Damassa 1979 Plate 2, figures 4-6

Remarks: Forms of the species recorded herein resemble the Californian forms recorded by Damassa, except that the English forms are more roundish and lack polar prominences or possess only a minor apical horn, generally narrower paracingulum and parasulcus, and up to two parasulcal plates only have been recognized. Both forms lack parasutural septa as char- acteristic of the genus and instead possess free pan- dasutural areas and occur in the Middle Eocene.

fix implying likeness; refers to its fig-shaped antapical process.

Diagnosis: Cyst subspherical, skolochorate and biphragmal; phragma adpressed; periphragm chagrinate or reticulate; many nontabular tubular processes tapering from broad circular bases to narrow necks before ending in distal aculeation or wider rims, proximally closed, distally open but rarely a few processes closed, a few neighboring pairs sometimes proximally joined; antapical process inflated, distinctively broad with biconvex ambitus in all lateral views with figlike appearance. Antapical process rises from a circular base, proximally closed, distally open but constricted with maximum width at base or mid-length; archeopyle apical type tA.

Types: Holotype: Slide BB-24(2),P35.2; Bed E6, Earn- ley Formation, Middle Eocene. Paratype: Slide BB- 23(1),F42.2.

Dimensions: Holotype: cyst body 28 x 36 /,m (without operculum), length of processes 15-17 /m, length of antapical process 21 A/m, maximum width of antapical process 20 /m. Range: cyst length 37(33)28 A/m, breadth 41(35)29 /m, length of processes 1 1-19 /Am, length of antapical process 21(19)17 gim, maximum width of antapical process 20(18)16 /m. Speci- mens measured: 10.

Occurrence: BB-1 9-BB-31. Other occurrences: Shap- ley Heath, Egem.

Remarks: The species has been previously recorded by a few workers as D. colligerum and it resembles that species except in the morphology of the antapical process. It is bell-shaped or cylindro-conical in D. colligerum, but it is fig-shaped with biconvex ambitus in all lateral views in D. ficusoides. The latter is separated because of its stratigraphic significance, and it is stratigraphically younger.

Fibrocysta Stover and Evitt 1978

Type species: Fibrocysta bipolare (Cookson and Ei- Diphyes Cookson 1965 senack) Stover and Evitt 1978.

Type species: Diphyes colligerum (Deflandre and Cookson) Cookson 1965.

Diphyes ficusoides Islam, n. sp. Plate 2, figures 8-9

Hystrichosphaeridium colligerum Deflandre and Cookson.-ROZEN 1965, p. 301, pl. 1, figs. 7-8, text-figs. 9-10. Late Eocene.- MORGENROTH 1966, p. 29, pl. 8, figs. 1-2. (?late) Early Eocene.

Diphyes colligerum (Deflandre and Cookson).-COOKSON 1965, p. 86, pl. 9, figs. 1-7, 10-12. Late Eocene.-MANUM 1976, p. 902, pl. 3, fig. 15. Middle Eocene.

Derivation of name: Latin: ficus = fig; -oides = a suf-

Fibrocysta exiguapicis Islam, n. sp. Plate 2, figures 10-11

Derivation of name: Latin: exiguus = short, poor, meager; apicis = apex, top; refers to its apical process lacking prominence.

Diagnosis: Cyst ellipsoidal, up to 2 g/m thick, skolochorate and strongly fibroreticulate; many nontabular fibrous processes, solid, thick and stout, proximally broad and frequently joined together up to about mid- length, tapering to bifid, branched or aculeate distal extremities; apical prominence indicated by group of

338


proximally joined processes or short blunt apical horn; antapical prominence similar or absent; archeopyle precingular type P.

Types: Holotype: Slide BB-20(1),R41.1; Bed E2, Earn- ley Formation, Early Eocene. Paratype: Slide BB- \2 20(2),Y45.1.

Dimensions: Holotype: cyst body 54 x 49 /m, length of processes 19-23 ~m. Range: cyst length 62(53)47 5" 4" 3" \ /um, breadth 52(48)44 /m, length of processes 14-23 ,um. Specimens measured: 10.//

"

//

//

4 c \\ 3c ( Occurrence: BB-20. // _ __ Remarks: This species differs from others of the ge- \ nus in possessing thick and stout processes that are frequently proximally joined, and less prominent apical 4 3" / 2"/ and antapical features. The antapical feature is often / absent.

Ginginodinium Cookson and Eisenack 1960, emend. Lentin and 2 | Williams 1976

Type species: Ginginodinium spinulosum Cookson and Eisenack 1960.

Dorsal view

?Ginginodinium claustrum Islam, n. sp. pr Plate 2, figures 12-14; text-figure 6

Derivation of name: Latin: claustrum = barrier, wall; refers to penitabular septa.

Diagnosis: Cyst dorsoventrally compressed peridi-1 < nioid, bearing short apical horn with blunt tip, acavate, proximochorate and biphragmal; endophragm chagrinate or microreticulate; periphragm chagrinate; peni- \ tabular septa of variable heights not exceeding 5 /m," 2 with variable distal indentations, lying too close to para- , // sutures to look parasutural in location; paratabulation 6 / - 4', 3a, 7", 6c, 5"', 2"", 1-3s; critically located pos- \ c 2 terior septa often resembling antapical horns, which / \| \ T ~

are absent; a few forms with divided septa, resem- s

bling discrete processes; archeopyle intercalary type\\ \ \ / 31/31 with free opercular pieces. 6c

Types: Holotype: Slide BB-12(1),G38.1; Bed W12, \\ / Wittering Formation, Early Eocene. Paratype: Slide BB- 12(1),P42.3.

Dimensions: Holotype: cyst body 45 x 40 ,/m, length of apical horn 6 g/m. Range: cyst length 48(38)32 ,/m, Ventral view breadth 48(39)31 g/m, length of apical horn 8(6)4 ,/m. TEXT-FIGURE 6 Specimens measured: 12. ?Ginginodinium claustrum Islam, n. sp. Camera lucida sketch of the

holotype. Occurrence: BB-11-BB-31.

Remarks: This species differs from others of the ge- Homotryblium Davey and Williams 1966

nus in possessing closely lying penitabular septa and in the absence of intratabular ornamentation. Its ge- Type species: Homotryblium tenuispinosum Davey and neric allocation remains tentative for the latter. Williams 1966.

339

II


Homotryblium deconinckii Islam, n. sp. Plate 3, figures 1-3

Schematophora speciosa Deflandre and Cookson.-DE CONINCK 1976, p. 104, pi. 18, figs. 24-25. Early Eocene.

Litosphaeridium luteticus GRUAS-CAVAGNETTO 1976, pl. 2, figs. 9-10. Middle Eocene.

Homotryblium sp. 1 DE CONINCK 1977, p. 41, pl. 5, fig. 17. Early Eocene.

Derivation of name: In honor of Jan De Coninck, a dedicated worker in fossil dinoflagellates at the La- boratorium voor Paleontologie, Rijksuniversiteit Gent, Belgium, who first recorded this species.

Diagnosis: Cyst ellipsoidal, proximochorate and biphragmal; periphragm chagrinate; intratabular hollow processes proximally circular or oval and closed and distally open and entire always with either flaring or constricting tendency, occasionally possessing minute distal spinules, generally broader than long but sometimes as long as broad; paratabulation observed from one process per paraplate including 6c, 6"', 1 p, ps, 1 ""; archeopyle epicystal, an operculum not seen but isolated paraplates found could be opercular pieces.

Types: Holotype: Slide BB-24(1),U33.3; Bed E5, Earn- ley Formation, Middle Eocene. Paratype: Slide BB- 24(1),F33.4.

Dimensions: Holotype: cyst body 21 x 40 /m (without operculum), length of processes 4-5 gm, breadth of processes 9-15 /um. Range: cyst length 21-26 /m (2 specimens), breadth 44(40)36 ,um, dorsoventral thickness 30-35 /um (2 specimens), length of processes 1-9 /m, breadth of processes 5-15 ,um. Spec- imens measured: 4.

Occurrence: BB-24.

Remarks: This species differs from others of the genus, particularly from Homotryblium abbreviatum Ea- ton 1976, to which it is most similar, in possessing typically short, broader than long processes with ten- dencies to constrict or flare distally.

Homotryblium umbellatum Islam, n. sp. Plate 3, figures 7-8

Derivation of name: Latin: umbella = umbrella; refers to the umbrella-like distal ramification of its processes.

Diagnosis: Cyst ellipsoidal, skolochorate and biphragmal; periphragm chagrinate; intratabular tubular processes with wider circular or oval bases tapering to narrower necks before distally ramifying into circular umbrella-like membranous expansions bearing six equally spaced spinules at extremities, sometimes re- curved; frequently "umbrella" is deformed; processes open at both ends; paratabulation observed from one process per paraplate defining 6c, 6"', Ip, ps, 1"";

archeopyle epicystal, operculum not seen but isolated paraplates found could be opercular pieces.

Types: Holotype: Slide BB-20(1),T34.1; Bed E2, Earn- ley Formation, Early Eocene. Paratype: Slide BB- 22(2),P41.2.

Dimensions: Cyst body 30 x 42 /um (without operculum), length of processes 15-18 ,um. Range: cyst breadth 42(40)36 /m, dorsoventral thickness 34(32)31 /tm, length of processes 9-18 /,m. Specimens measured: 5.

Occurrence: BB-20-BB-24.

Remarks: This species differs from others of the genus, particularly from Homotryblium pallidum Davey and Williams 1966 and H. tenuispinosum, to which it bears some resemblance in possessing the umbrella- like distal ramifications of the processes.

Homotryblium sp. A Plate 3, figure 9

Description: This species is characterized by short intratabular processes which are tubular, thinly tubular or solid; all types may be present in the same specimen with tubular ones, if present, mostly posteriorly placed. The archeopyle is epicystal.

Hystrichokolpoma Klumpp 1953, emend. Williams and Downie 1966a

Type species: Hystrichokolpoma cinctum Klumpp 1953.

Hystrichokolpoma manipulatum Islam 1983 Plate 3, figure 12

Description: The cyst is characterized by broad epi- and hypocystal processes distally divided into tubules which are generally open and appear to have resulted from proximal fusion of thinner tubular processes similar to those of Diphyes colligerum, which are still there as discrete paracingular processes.

?Hystrichokolpoma petasatum Islam, n. sp. Plate 3, figures 4-5

Derivation of name: Latin: petasatus = with a hat on; refers to its anterior process morphology.

Diagnosis: Cyst ellipsoidal, skolochorate and biphragmal; endophragm chagrinate or weakly reticulate; periphragm chagrinate; intratabular hollow processes, epi- and hypocystal processes broad with subquadran- gular bases, generally tapering rapidly to narrow tubes and continuing to entire or wider serrate distal extremities; paracingular processes tubular and distally open; all processes proximally closed; four apical processes proximally joined together like a crown bearing distal tubules; antapical process longest, distally suddenly tapering to open tubule bearing spinules; paratabula-

340


tion 4', 6", 6c, 6"', ?1p, 1"", xs; archeopyle apical type 4A.

Types: Holotype: Slide BB-13(1),Q42.4; Bed W13, Wittering Formation, Early Eocene. Paratype: Slide BB- 31(2),P48.2.

Dimensions: Holotype: cyst body 42 x 33 gm, length of processes 15-20 /im, length of antapical process 25 igm. Range: cyst length 50(45)42 ,/m, breadth 40(38)33 gm, length of processes 15-22 /m, length of antapical process 30(27)25 /im. Specimens measured: 4.


Remarks: The generic allocation of the species is made on the basis of general morphology including two types of processes and apical archeopyle, but is tentative because of the peculiarity involving the apical series of processes which are proximally joined to look like a crown, and this is how it differs from other species of the genus. However, in process morphology, it resembles Hystrichokolpoma rigaudiae Deflandre and Cookson 1955 for which the processes of the operculum have not been described. Other species of this genus with operculum known do not, however, show the peculiar proximal joining of apical processes as in this species.

Lingulodinium Wall 1967, emend. Wall and Dale in Wall, Dale and Harada 1973

Type species: Lingulodinium machaerophorum (De- flandre and Cookson) Wall 1967.

Lingulodinium funginum (Morgenroth) Islam, n. comb. Plate 3, figure 10

Baltisphaeridium funginum MORGENROTH 1966, p. 17, pl. 3, figs. 7-8. Early Eocene.

Lingulodinium machaerophorum (Deflandre and Cookson) Wall.- DE CONINCK 1976, p. 72, pi. 11, figs. 21-22 only. Early Eocene.

Emended diagnosis: Cyst subspherical, proximochorate and biphragmal; periphragm chagrinate or granulate; numerous short, hollow, nontabular processes with closed circular or oval bases and bluntly rounded, bulbous or truncate closed distal tips, frequently distal "bulbs" broader than process stems and mushroom- like; small spines sometimes present between processes; archeopyle precingular type 2P-5P, operculum free.

Remarks: Morgenroth's (1966) observation on its py- lome with zigzag margin as being very similar to that in Baltisphaeridium machaerophorum Deflandre and Cookson 1955 is supported by observations in this study and is sufficient reason for the present generic transfer of the species. It differs from other species

of Lingulodinium in possessing mushroom-like or distally truncate processes.

Operculodinium Wall 1967

Type species: Operculodinium centrocarpum (De- flandre and Cookson) Wall 1967.

Remarks: Stover and Evitt (1978) characterized the genus as possessing nonfibrous processes (pp. 154, 178), but at the same time transferred Cordosphaeridium divergens (Eisenack) Eisenack 1963 and Cordosphae- ridium xanthium Benedek 1972, which apparently pos- sessed fibrous processes, to this genus. It is observed that Operculodinium-like forms possess both fibrous and nonfibrous processes with various ranges of mix- ing and gradations of the two types in the same specimen. Frequently it is difficult to distinguish the two types of processes under optical microscopes. No useful purpose is believed to be served in separating them at the present stage. It is, therefore, recommended that the genus Operculodinium be considered as possessing both fibrous and nonfibrous processes until a strong case can be made for the separation of fibrous forms in a separate genus.

Operculodinium exquisitum Islam, n. sp. Plate 4, figure 8

Derivation of name: Latin: exquisitus = excellent, ex- quisite.

Diagnosis: Cyst subspherical, sometimes broader than long, proximochorate to skolochorate; endophragm reticulate; periphragm reticulate/fibroreticulate; numerous nontabular fibrous processes generally solid but sometimes partly proximally hollow while distally closed or open, broader at bases, tapering to thin necks just below distal aculeation; paracingulum sometimes indicated by rows of processes; archeopyle precingular type P.

Type: Holotype: Slide BB-30(2),K45.2; Bed S2, Selsey Formation, Middle Eocene.

Dimensions: Holotype: cyst body 68 x 73 gm, length of processes 12-17 gm. Range: cyst length 78(61)46 gim, breadth 83(61)36 gm, length of processes 7-22 gim. Specimens measured: 10.


Remarks: This species differs from Operculodinium microtriaina (Klumpp) Islam 1983, 0. uncinispinosum (De Coninck) Islam, n. comb., and 0. centrocarpum in possessing wholly fibrous and partly hollow processes. It resembles 0. nitidum Islam 1983 most closely but differs in being much larger, lacking proximal process connections and possessing partly hollow processes; it is also stratigraphically younger.

341


Operculodinium severinil (Cookson and Cranwell) Islam, n. comb. Plate 4, figures 1-2

Baltisphaeridium severinii COOKSON and CRANWELL 1967, p. 208, pl. 3, figs. 1-2. Early Eocene.-DE CONINCK 1969, p. 51, pl. 15, figs. 62-64. Early Eocene.

Eocladopyxis sp. A DE CONINCK 1977, p. 41, pi. 1, figs. 13-14. Middle Eocene.

Operculodinium sp. B GOODMAN 1979, p. 183, pl. 1, fig. 9. Early Eocene.

Impletosphaeridium severinii (Cookson and Cranwell).-LIENGJAR- ERN ET AL. 1980, p. 486. Late Eocene.

Emended diagnosis: Cyst subspherical to ellipsoidal, proximochorate to skolochorate and biphragmal; periphragm chagrinate, granulate or reticulate; numerous nontabular solid processes proximally conical, tapering to mid-length and continuing as thin slender forms to acuminate tips; processes sometimes flexible; ar-

cheopyle precingular type P but frequently indistinguishable.

Remarks: The present generic reallocation and emendation of the diagnosis of the species comes about because of the presence of a precingular type P ar-

cheopyle in some specimens. It differs from other species of the genus in process morphology by which it resembles Eocladopyxis Morgenroth 1966 which possesses an epicystal archeopyle. Liengjarern et al. (1980) mentioned the possible presence of such ar-

cheopyle sutures and hence projected the possibility of a "retransfer" to Eocladopyxis. However, in the present study and also in Goodman (1979), the precingular archeopyle of the species is quite clearly shown (pl. 4, fig. 1 shows some mechanical damage).

Operculodinium uncinispinosum (De Coninck) Islam, n. comb. Plate 3, figure 6

Cordosphaeridium palmatum (White).-DE CONINCK 1965, p. 32, pl. 6, figs. 8, 10. Early Eocene.

Cordosphaeridium uncinispinosum DE CONINCK 1969, p. 32, pl. 9, figs. 6-8. Early Eocene; 1976, p. 81, pl. 14, figs. 4-12. Early Eocene.

Remarks: The generic reallocation of the species is made because it possesses nontabular processes which are partly fibrous and partly nonfibrous, and a

precingular type P archeopyle. The processes are dis-

tally aculeate with generally more than three and rarely less than six aculei, and this is how it differs from 0. microtriaina, which also possesses generally shorter

processes. These differences seem insufficient to jus- tify the maintenance of the two species, but the matter should be left for further observation.

Paucisphaeridium Bujak, Downie, Eaton and Williams 1980c

Type species: Paucisphaeridium inversibuccinum (Davey and Williams) Bujak et al. 1980c.

Paucisphaeridium cylindratum Islam, n. sp. Plate 1, figures 12-14

Derivation of name: Latin: cylindratus = cylindrical; refers to its process morphology.

Diagnosis: Cyst spherical to subspherical, skolochorate and biphragmal; both phragma chagrinate; intratabular processes broad to very broad, cylindrical, proximally little wider and generally connected to one another sometimes with high rising membranes; processes distally open, wider, entire or minutely indented; one process per paraplate giving paratabulation of ?4', 5-6", Oc, 6-7"', 0"", the pre- and postcingular processes together generally 12; archeopyle apical type tA.

Types: Holotype: Slide BB-20(1),K33.2; Bed E2, Earn- ley Formation, Early Eocene. Paratype: Slide BB- 24(2),E36.2.

Dimensions: Holotype: cyst diameter 19 ,/m, length of processes 9-10 g/m, breadth of processes 4-11

,/m. Range: cyst diameter 19(17)16 ,/m, length of processes 5-10 ,m, breadth of processes 3-11 ,/m. Specimens measured: 5.

Occurrence: BB-20-BB-24. Other occurrence: Shep- pey.

Remarks: This species differs from P. inversibuccinum in possessing broad cylindrical processes.

Polysphaeridium Davey and Williams 1966, emend. Bujak, Down- ie, Eaton and Williams 1980c

Type species: Polysphaeridium subtile Davey and Wil- liams 1966, emend. Bujak et al. 1980c.

Polysphaeridium biformum Islam, n. sp. Plate 4, figures 3, 6

Derivation of name: Latin: bi- = two, double; forma =

form, shape; refers to its two types of processes.

Diagnosis: Cyst subspherical to ellipsoidal, skolochorate and biphragmal; periphragm chagrinate; numerous nontabular processes of two distinct types: tubular with wider ends and distally open, which are similar to those of P. subtile, and solid, which are proximally thicker and distally entire, bifurcate or with wider fenestrate ramifications, latter type preferably placed in paracingular areas or elsewhere; some transitional types proximally hollow while solid in remain- ing length; solid and partly solid processes longer than tubular ones; archeopyle epicystal type tAtP, most specimens split.

Types: Holotype: Slide BB-21(1),M46.3; Bed E4, Earn-

ley Formation, Middle Eocene. Paratype: Slide BB- 22(2),L38.4.

342


Dimensions: Holotype: cyst body 52 x 42 /tm, length of processes 11-19 /um. Range: maximum median cyst diameter 47(45)42 z/m, length of processes 10- 20 /m. Specimens measured: 10. / \

Occurrence: BB-22-BB-23, peak BB-22, 31.5%.

Remarks: This species differs from others of the genus in possessing two types of processes, the length / of the longer ones approaching half the median di- / / I ameter of the cyst. It is related to P. subtile through intermediate and transitional forms found in the same preparations. 4c 3 2c

Polysphaeridium subtile Davey and Williams 1966, emend. Bujak \ \ ,, \\ -/ / 2 etal. 1980c c 3

Hystrichosphaeridium zoharyi ROSSIGNOL 1962, p. 132, pl. 2, fig. \ / 10. Pleistocene.

Hemicystodinium zoharyi (Rossignol).-WALL 1967, p. 110. Qua- ternary.

Polysphaeridium zoharyi (Rossignol).-BUJAK ET AL. 1980c, p. 34.

Remarks: Emendation of Polysphaeridium by Bujak et al. (1980c) rendered the genus Hemicystodinium Wall Dorsal view 1967 congeneric with the former, but their types were retained as distinct species of Polysphaeridium. Prior to this emendation, some Eocene and most post- Eocene occurrences of the species were recorded as 4' Hemicystodinium zoharyi, which can hardly be distinguished morphologically from P. subtile. From an ex- amination of the figured holotypes of P. subtile and H. / // ? \ zoharyi, they are considered conspecific. This action / // credits P. subtile with an unbroken stratigraphic record 4" 5" -~ ) i from Late Cretaceous to Recent (Islam 1981). / ( , /.___ ,\

Polysphaeridium subtile subsp. ktana (Rossignol) Islam, n. comb. Plate 4, figure 7\\

Hystrichosphaeridium cf. intermedium ROSSIGNOL 1962, p. 132, pl. 2, fig. 9. Pleistocene.

Hystrichosphaeridium zoharyi var. ktana ROSSIGNOL 1964, p. 88, / pl. 2, figs. 6-7, 10; pl. 3, fig. 11. Pleistocene. \ s

Hystrichosphaeridium breviatum MORGENROTH 1966, p. 29, pl. 7, figs. 11-12. Early Eocene.-GRUAS-CAVAGNETTO 1968, p. 87, l pl. 12, figs. 7-10. Paleocene-Eocene. I

Hemicystodinium zoharyi subsp. ktana (Rossignol).-LENTIN and WILLIAMS 1973, p. 67.

Hemicystodinium sp. 2 CHATEAUNEUF 1980, p. 114, pi. 24, fig. 4. Ventral view Late Eocene.

TEXT-FIGURE 7

Remarks: Generic reallocation of the subspecies be- Thalassiphora decrementa Islam, n. sp. Camera lucida sketch of the Remar. Genesar rue all ocaonymiza of on of Heml'cy holotype. Paratabulation partly schematized from observations on

came necessary due to synonymization of Hemicys- many specimens. todinium zoharyi to P. subtile. Hystrichosphaeridium breviatum is considered a junior synonym of this subspecies.

Thalassiphora decrementa Islam, n. sp. Plate 4, figures 4-5; text-figure 7

Thalassiphora Eisenack and Gocht 1960, emend. Gocht 1968 Latin: decrementus = a diminu- Derivation of name: Latin: decrementus = a diminu- Type species: Thalassiphora pelagica (Eisenack) Ei- tion, lessening; refers to its reduced pericoelar sepa- senack and Gocht 1960. ration.

343


Diagnosis: Cyst ellipsoidal to subspherical, proximate, camocavate and biphragmal; sometimes possessing only an apical, or an apical, antapical and two paracingular bulges or protrusions in the pericyst; endocyst sometimes with polar protrusions only; endophragm 1 A/m thick and reticulate; periphragm very thin, punc- to-reticulate, adpressed to endophragm on dorsal side of cyst and separated elsewhere to a maximum pericoelar separation of 12 LTm, sometimes almost no cavation in extreme forms but minor partial cavation always; periphragmal thickening, defining paratabulation of 4', ?la, 5", 4c, 5"', ?lp, 1"", xs; archeopyle precingular type P representing paraplate 3", operculum attached.

Type: Holotype: Slide BB-25(3),L30.2; Bed E7, Earnley Formation, Middle Eocene.

Dimensions: Holotype: endocyst 68 x 57 A/m, maximum pericoelar separation 11 g/m. Range: endocyst length 78(69)54 ,/m, breadth 78(62)52 ,m, maximum pericoelar separation 12(6.4)5 /m, length of periapical horn 0-14 ,m. Specimens measured: 13.

Occurence: BB-19-BB-29. Other occurrence: Shapley Heath.

Remarks: This species differs from others of the genus in the reduced pericoel. Its periphragm resembles that of Thalassiphora patula (Williams and Downie) Bu- jak et al. 1980c and it is a derivative of that species resulting from progressive reduction of pericoel and development of polar and lateral features. Maximum pericoelar separation of 12 g/m is set for delimiting the two species. Near-acavate forms resemble Spongo- dinium Deflandre 1936, emend. Stover and Evitt 1978 and Muratodinium Drugg 1970 but these genera possess autocysts only.

The development of T. decrementa, n. sp. is different from and apparently unconnected with that of T. pelagica as discussed by Gocht (1968). According to Gocht, T. pelagica developed with an increasing separation of the two phragma, and I agree with Eaton (1976) that Gocht's forms of initial and intermediate stages should be excluded from T. pelagica. Gocht's ideas have been re-emphasized recently (Benedek and Gocht 1981), but it is felt that the above observation still holds good in view of the present state of the fossil dinoflagellate taxonomy. Thalassiphora decrementa, on the other hand, has evidently developed by progressive reduction of the pericoel and is connected to T. patula, and is stratigraphically younger and significant.

Trivalvadinium Islam, n. gen.

Derivation of name: Latin: tri = three; valva = leaf of a folding door; refers to its archeopyle involving three anterior intercalary paraplates.

Diagnosis: Cyst peridinioid and roundly pentagonal to subspherical; horns, if present, vestigial; laterally to dorsoventrally compressed; proximochorate; acavate to narrowly circumcavate when possessing two mildly ornamented phragma; numerous or relatively fewer nontabular processes, solid, tubular or thinly tubular; archeopyle intercalary type 31/31 or 31 when an autocyst, operculum free, opercular pieces not found.

Type species: Trivalvadinium formosum Islam, n. sp.

Remarks: The genus resembles Apectodinium (Costa and Downie) Lentin and Williams 1977 but differs in possessing a 31 intercalary archeopyle. However, from their co-occurrence and abundance, the two genera are believed to be related, and both genera favor a

PLATE 1

All x 1000, or as otherwise mentioned

1-3 Achilleodinium fibrapendiculum Islam, n. sp. x 750. 1-2, holotype, slide BB-31(3),L40.4; 3, paratype, slide BB-30(3),V47.2.

4 Cordosphaeridium minus (Morgenroth) Is- lam, n. status Slide BB-23(2),E39.2, x 750.

5 Areosphaeridium sp. A Slide BB-24(1),P43.3.

6-7 ?Alterbia bicellula Islam, n. sp. 6, holotype, slide BB-29(1),C42.4; 7, paratype, slide BB-29(2),V49.4.

8-9 Apectodinium folliculum Islam, n. sp. 8, holotype, slide BB-27(1),P42.1. 9, paratype, apex to top right, slide BB-12(1),M42.2, a rounded pentagonal form.

10-11 ?Alterbia earnleyense Islam, n. sp. 10, holotype, slide BB-29(1),M47.4. 11, paratype, slide BB-28(1),030.4.

12-14 Paucisphaeridium cylindratum Islam, n. sp. 12, holotype, slide BB-20(1),K33.2; 13-14, paratype, slide BB-24(2),E36.2.

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brackish-water environment. Other genera with 31 ar- cheopyles, viz. Trithyrodinium Drugg 1967, emend. Lentin and Williams 1976 differ in lacking processes, and Ginginodinium Cookson and Eisenack 1960, emend. Lentin and Williams 1976 in possessing distinct paratabulation.

Trivalvadinium formosum Islam, n. sp. Plate 4, figure 9

Derivation of name: Latin: formosus = comely, beau- tifully formed.

Diagnosis: Cyst peridinioid, rounded pentagonal, laterally to dorsoventrally compressed, proximochorate, acavate, cornucavate or discontinuously circumcavate, and biphragmal; both phragma mildly chagrinate; horns, if present, vestigial, apical and two antapical horns only; many or relatively fewer solid, tubular or thinly tubular nontabular processes all distally aculeate and open when hollow, sometimes proximally joined in pairs; paracingulum sometimes partially indicated by periphragmal folds; archeopyle intercalary type 31/31, sometimes enlarged with irregular margins.

Type: Holotype: Slide BB-26(1),T35.2; Bed E8, Earnley Formation, Middle Eocene.

Dimensions: Holotype: cyst body 55 x 56 /m, length of processes 5-10 Am. Range: cyst length 58(53)47 /tm, breadth 60(52)42 ,um, length of processes 3-11 gm. Specimens measured: 10.

Occurrence: BB-10-BB-30, peak BB-28, 11%. Other occurrences: Baughurst, Chobham Common, Shep- pey.

Remarks: In process morphology, the species resembles Apectodinium sumissum Harland 1980 and A. folliculum Islam, n. sp. but differs in possessing 31/31 ar-

cheopyle. The species appears to favor a brackish- water environment.

Wetzeliella Eisenack 1938, emend. Lentin and Williams 1976

Type species: Wetzeliella articulata Eisenack 1938.

Wetzeliella astroides Islam, n. sp. Plate 3, figure 11

Derivation of name: Latin: astra = star; -oides = resembling, having the form of; refers to its stellate form.

Diagnosis: Pericyst compressed peridinioid with apical, two paracingular, and two antapical horns, all more or less equal in length and placed more or less equidistant from one another on the ambitus in a diverging attitude, thus resembling a star; endocyst generally rounded pentagonal but sometimes subspherical, frequently tending to intrude into the bases of horns where phragmal thickening, granulation or accumula- tion of spongy substances commonly occur; both phragma thin and psilate or mildly chagrinate; proximochorate and circumcavate; paracingular horns distally notched while others generally pointed, apical horn sometimes distally blunt; many nontabular tubular processes open at both ends and distally aculeate; archeopyle intercalary type I/I, representing paraplate 2a with quadra style, operculum attached.

Type: Holotype: Slide BB-22(1),C32.4; Bed E4, Earn- ley Formation, Early Eocene.

Dimensions: Holotype: pericyst 130 x 130 ,um, endocyst 80 x 78 /,m, length of horns 24-30 /tm, length of processes 5-8 /,m. Range: pericyst length 156- (131)120 ,/m, breadth 164(117)114 /,m; endocyst length 92(76)64 /m, breadth 94(74)61 ,/m; length of horns 18-31 ,/m, length of processes 3-10 /tm. Spec- imens measured: 13.

PLATE 2


1-2 Cleistosphaeridium spinulastrum Islam, n. sp. 1, holotype, slide BB-24(2),T35.2; 2, paratype, slide BB-24(1),K46.4.

3, 7 Cleistosphaeridium selseyense Islam, n. sp. 3, holotype, slide BB-31(2),S38.4; 7, paratype, slide BB-31(1),L37.3.

4-6 Danea impages Damassa 1979 4, slide BB-26(1),J43.1, x 750; 5-6, slide BB- 26(2),K32.1, x 500.

8-9 Diphyes ficusoides Islam, n. sp. 8, holotype, slide BB-24(2),P35.2; 9, paratype, slide BB-23(1),F42.2.

10-11 Fibrocysta exiguapicis Islam, n. sp., x 750. 10, holotype, slide BB-20(1),R41.1; 11, paratype, slide BB-20(2),Y45.1.

12-14 ?Ginginodinium claustrum Islam, n. sp. 12-13, holotype, slide BB-12(1),G38.1; 14, paratype, slide BB-12(1),P42.3.

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Occurrence: BB-20-BB-31, peak BB-23, 3.5%.

Remarks: This species differs from others of the genus in its typical stellate morphology derived from five periphragmal horns that are of more or less equal lengths and equidistant from one another. Wetzeliella articulata resembles somewhat this species but differs in possessing a shorter apical horn and relatively closely placed antapical horns, thus lacking a stellate morphology.

ACKNOWLEDGMENTS

The work was carried out at the Department of Ge- ology, University of Sheffield, supervised by Professor Charles Downie. Dr. C. King of Paleoservices Ltd. kindly accompanied me to Bracklesham Bay and helped locate the sample points. Dr. B. E. Balme, Head of the Department of Geology, University of Western Aus- tralia and Dr. J. F. Wiseman of Woodside Offshore Petroleum Pty Ltd. critically read an earlier text, suggested improvements and pre-reviewed the rewritten manuscript. Dr. Balme magnanimously offered facili- ties during the preparation of the manuscript. Dr. J. P. Bujak of Petro-Canada offered many valuable sugges- tions as the journal's reviewer which helped improve the manuscript. Professor Downie kindly paid the plate charges. I was in receipt of an award from the Asso- ciation of Commonwealth Universities during the work, and I am deeply indebted to all mentioned.

REFERENCES

BENEDEK, P. N., 1972. Phytoplanktonten aus dem Mittel- und Oberoligozan von Tonisberg (Niederrheingebiet). Palaeontograph- ica, Abt. B, 137:1-71, pls. 1-16.

BENEDEK, P. N., and GOCHT, H., 1981. Thalassiphora pelagica (Di- noflagellata, Tertiar): Electronenmikroskopische untersuchung und gedanken zur Palaobiologic. Palaeontographica, Abt. B, 180:39- 64, pls. 1-5.

BRISTOW, H. W., 1862. The geology of the Isle of Wight. Geol. Sur. U.K., Mem., 138 pp.

BUJAK, J. P., 1980. Dinoflagellate cysts and acritarchs from the Eocene Barton Beds of southern England. In: Bujak, J. P., Down- ie, C., Eaton, G. L., and Williams, G. L., Dinoflagellate cysts and acritarchs from the Eocene of southern England. Pal. Assoc. Lon- don, Spec. Paper Pal., 24:36-100.

BUJAK, J. P., DOWNIE, C., EATON, G. L., and WILLIAMS, G. L., 1980a. Stratigraphy. In: Bujak, J. P., Downie, C., Eaton, G. L., and Williams, G. L., Dinoflagellate cysts and acritarchs from the Eocene of southern England. Pal. Assoc. London, Spec. Paper Pal., 24: 9-15.

, 1980b. Dinoflagellate cyst zonation of the Eocene, southern England. In: Bujak, J. P., Downie, C., Eaton, G. L., and Williams, G. L., Dinoflagellate cysts and acritarchs from the Eocene of southern England. Pal. Assoc. London, Spec. Paper Pal., 24:15- 26.

, 1980c. Taxonomy of some Eocene dinoflagellate cyst species from southern England. In: Bujak, J. P., Downie, C., Eaton, G. L., and Williams, G. L., Dinoflagellate cysts and acritarchs from the Eocene of southern England. Pal. Assoc. London, Spec. Paper Pal., 24:26-36.

CHATEAUNEUF, J.-J., 1980. Palynostratigraphie et Paleoclimatolo- gie de I'Eocene superieur et de l'Oligocene du bassin de Paris (France). These de doctorat d'etat et Sciences Naturelles, a I'Uni- versite Pierre et Marie Curie, Paris, 383 pp., 31 pls.

COOKSON, I. C., 1965. Cretaceous and Tertiary microplankton from south-eastern Australia. Roy. Soc. Victoria, Proc., n. ser., 78:85- 93, pis. 9-11.

COOKSON, I. C., and CRANWELL, L. M., 1967. Lower Tertiary microplankton, spores and pollen grains from southernmost Chile. Micropaleontology, 13(2):204-216.

PLATE 3


1-3 Homotryblium deconinckii Islam, n. sp. 1-2, holotype, slide BB-24(1),U33.3; 3, paratype, slide BB-24(1),F33.4.

4-5 ?Hystrichokolpoma petasatum Islam n. sp. x 750. 4, paratype, slide BB-31(2),P48.2; 5, holotype, slide BB-13(1),Q42.4.

6 Operculodinium uncinispinosum (De Coninck) Islam, n. comb. Slide BB-11 (2),R46.2.

7-8 Homotryblium umbellatum Islam, n. sp. 7, holotype, slide BB-20(1),T34.1; 8, paratype, slide BB-22(2),P41.2.

9 Homotryblium sp. A Slide BB-13(2),K31.4.

10 Lingulodinium funginum (Morgenroth) Islam, n. comb. Slide BB-20(1),D34.2.

11 Wetzeliella astroides Islam, n. sp. Slide BB-22(1),C32.4. Holotype. x 500.

12 Hystrichokolpoma manipulatum Islam 1983 Slide BB-19(1),E49.1.

348

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COOKSON, I. C., and EISENACK, A., 1960. Microplankton from Aus- tralian Cretaceous sediments. Micropaleontology, 6(1):1-18, pis. 1-3.

COOPER, J., 1976. British Tertiary stratigraphical and rock terms.

Tertiary Res., Spec. Paper, 1:37 pp.

COSTA, L. I., and DOWNIE, C., 1976. The distribution of the dino-

flagellate Wetzeliella in the Palaeogene of north-western Europe. Palaeontology, 19:591-614.

COSTA, L. I., DOWNIE, C., and EATON, G. L., 1976. Palynostratig- raphy of some Middle Eocene sections from the Hampshire Basin

(England). Geol. Ass., Proc., London, 87:273-284.

CURRY, D., 1965. The Paleogene beds of south-east England. Geol. Ass., Proc., London, 76:151-173.

CURRY, D., ADAMS, C. G., BOULDER, M. C., DILLEY, F. C., EAMES, F. E., FUNNELL, B. M., and WELLS, M. K., 1978. A correlation of Tertiary rocks in the British Isles. Geol. Soc. London, Spec. Rept., 12:72 pp.

CURRY, D., KING, A. D., KING, C., and STINTON, F. C., 1977. The Bracklesham Beds (Eocene) of Bracklesham Bay and Selsey, Sus- sex. Geol. Ass., Proc., London, 88:243-254.

DAMASSA, S. P.., 1979. Eocene dinoflagellates from the coastal belt of the Franciscan Complex, Northern California. Jour. Pal., 53: 815-840.

DAVEY, R. J., 1969. The evolution of certain Upper Cretaceous Hys- trichospheres from South Africa. Palaeontologia Africana, 12:25- 31, pls. 1-4.

DAVEY, R. J., DOWNIE, C., SARJEANT, W. A. S., and WILLIAMS, G. L., 1966. Fossil dinoflagellate cysts attributed to Baltisphaeri- dium. In: Davey, R. J., Downie, C., Sarjeant, W. A. S., and Wil- liams, G. L., Studies on Mesozoic and Cainozoic dinoflagellate cysts. Brit. Mus. (Nat. Hist.), Bull. (Geol.), suppl. 3:157-175.

DAVEY, R. J., and VERDIER, J. P., 1973. An investigation of micro-

plankton assemblages from latest Albian (Vraconian) sediments. Rev. Espanola Micropal., 5:173-212, pls. 1-5.

DAVEY, R. J., and WILLIAMS, G. L., 1966. The genus Hystricho- sphaeridium and its allies. In: Davey, R. J., Downie, C., Sarjeant, W. A. S., and Williams, G. L., Studies on Mesozoic and Cainozoic

dinoflagellate cysts. Brit. Mus. (Nat. Hist.), Bull. (Geol.), suppl. 3: 53-106.

DE CONINCK, J., 1965. Microfossiles planctoniques du Sable ypresien a Merelbeke. Dinophyceae et Acritarcha. Acad. Roy. Belgique Cl. Sci., Mem., Coll. 8 (26-2):56 pp., 14 pls.

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PLATE 4


1-2 Operculodinium severinii (Cookson and Cran- well) Islam, n. comb. 1, slide BB-27(1),V34.4; 2, slide BB-28(1),W43.3.

3, 6 Polysphaeridium biformum Islam, n. sp. 3, paratype, slide BB-22(2),L38.4; 6, holotype, slide BB-21(1),M46.3.

4-5 Thalassiphora decrementa Islam, n. sp. Holotype, slide BB-25(3),L30.2. x 750. 4, optical view; 5, dorsal view.

7 Polysphaeridium subtile subsp. ktana (Rossi- gnol) Islam, n. comb. Slide BB-22(2),V33.3.

8 Operculodinium exquisitum Islam, n. sp. Holotype, slide BB-30(2),K45.2, x 500.

9 Trivalvadinium formosum Islam, n. sp. Holotype, slide BB-26(1),T35.1.

350

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EISENACK, A., and GOCHT, H., 1960. Neue Namen for einige Hys- trichospharen der Bernsteinformation Ostpreussens. Neues Jahrb. Geol. Pal., Monatsh., 11:511-518.

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GOODMAN, D. K., 1979. Dinoflagellate "Communities" from the Lower Eocene Nanjemoy Formation of Maryland, U.S.A. Palynol- ogy, 3:169-190.

GRUAS-CAVAGNETTO, C., 1968. Etude palynologique des divers gisements de Sparnacien du bassin de Paris. Soc. Geol. France, Mem., n. ser., 47(2), 110:1-114, pis. 1-18.

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HARLAND, R., 1980. The Wetzeliella (Apectodinium) homomorpha plexus from the Palaeocene/earliest Eocene of north-west Eu- rope. IV Internat. Palynol. Congr., Lucknow 1976-77, 2:59-70, pls. 1-2.

ISLAM, M. A., 1981. Early and Middle Eocene organic microplankton of the Anglo-Belgian Basins. Ph.D. thesis, unpublished, Univ. Sheffield, U.K., 368 pp., 47 pis.

, 1983. Dinoflagellate cysts from the Eocene cliff sections of the Isle of Sheppey, southeast England. Rev. Micropal., 25(4): 231-250, pls. 1-4.

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Manuscript received September 17, 1982. Manuscript accepted March 1, 1983.

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