Order Didelphimorphia, Family Didelphidae—American opossums Virginia opossum—Didelphis virginiana

1) dental formula = I5/4 C1/1 P3/3 M4/4 2) prominent sagittal crest 3) fenestrated palatines 4) angular process medial from mandible

Order Soricomorpha, Family Soricidae—shrews

1) incomplete zygomatic arches 2) at least some teeth tipped with red or black 3) cheek teeth dilambdodont 4) bicuspid I1

pygmy shrew—Sorex (Microsorex) hoyi

1) only 3 unicuspids readily visible from side

1 2 4

water shrew—Sorex palustris

1) skull length > 19 mm (not in key) 2) rostrum short, relative to S. bendirii

Pacific water shrew—Sorex bendirii

1) skull length > 19 mm (not in key) 2) rostrum long, relative to S. palustris

Sorex bendirii

Sorex palustris

arctic shrew—Sorex arcticus masked shrew—Sorex cinereus tundra shrew—Sorex tundrensis

1 2 3 4

1) 3rd unicuspid not smaller than 4th

Sorex cinereus Sorex arcticus

Sorex tundrensis

dusky shrew—Sorex monticolus Trowbridge’s shrew—Sorex trowbridgii

vagrant shrew—Sorex vagrans

1) 3rd unicuspid smaller than 4th

4 3

Sorex trowbridgii

Sorex vagrans Sorex monticolus

Order Soricomorpha, Family Talpidae—moles

1) complete zygomatic arches 2) teeth entirely white

shrew-mole—Neurotrichus gibbsii

1) dentition: I3/3 C1/1 P2/2 M3/3 2) auditory bullae incompletely formed

coast mole—Scapanus orarius

1) dentition: I3/3 C1/1 P4/4 M3/3 2) auditory bullae completely formed 3) skull < 40 mm

coast mole—Scapanus orarius

Townsend’s mole—Scapanus townsendii

1) dentition: I3/3 C1/1 P4/4 M3/3 (usually) 2) auditory bullae completely formed 3) skull > 40 mm

Townsend’s mole—Scapanus townsendii