36 



NOETH AMEEICAN FAUNA. 



[NO. 39. 



Thomomysfuscus grouj) (pp. 126-131): 



Thomomys fuscus fuscus Merriam Head of Big Lost River, Idaho. 



fuscus saturatus Bailey Silver (near Saltese), Mont. 



fuscus loringi Bailey South Edmonton, Alberta, Canada. 



fuscus myops Merriam Conconully, Wash. 



Aespems Merriam Tillamook, Or eg. 



Key to Groups of Related Species. 



a^. Rostrum deep and evenly sloping in front of upper molars. 



h^. Pterygoids concave on inner surface and convex on outer; mammse in 4 pairs, 



bulbivorus group (p. 40). 



b^. Pterygoids flat and straight. 



Mammae in 3 pairs (inguinal, 2-2; pectoral, 1-1) umbrinus group (p. 89). 



c^. Mammse in 4 pairs (inguinal, 2-2; pectoral, 2-2). 



d^. Skull short and wide; color mainly dark or light ochraceous, 



bottae group (p. 45). 



d^. Skull not conspicuously short and wide. 



e^. Skull long and narrow; color dark alpinus group (p. 63). 



e^. Skull not conspicuously long and narrow; color mainly pale. 

 Color pale buffy yellowish, or gray and black. 

 g^. Color buffy or yellowish (except apache). . . perpallidus group (p. 68). 



g'^. Color gray and black townsendi group (p. 42). 



/2. Color tawny (light or dark tawny) fulvus group (p. 80). 



a^. Rostrum slender, abruptly arched in front of upper molars. 



h\ Mammse in 6 pairs or more (inguinal, 2-2; abdominal, 2-2; pectoral, 2-2), 



talpoides group (p. 96). 



b^. Mammae in 4 or 5 pairs. 



c\ Mammae in 5 pairs (inguinal, 2-2; pectoral, 3-3) fossor group (p. 111). 



c^. Mammse in 4 pairs (inguinal, 2-2; pectoral, 2-2). 



d^. Ears rather large and rounded at tips douglasi group (p. 116). 



d^. Ears large or small and pointed at tips. 



e^. Ears relatively large and pointed monticola group (p. 121). 



e^. Ears relatively small and pointed fuscus group (p. 126). 



'Key to Species and Subspecies of Thomomys. 



[Measurements in millimeters.] 



a^. Size large; hind foot of 38 or more. 



5^ Color uniformly dark sooty brown above and below; hind foot of c? 40 or more, 



bulbivorus (p. 40). 

 b'^. Color gray or black (dichromatic); hind foot of c? 38, of $ 35. 



c\ Color in gray phase dark buffy gray townsendi (p. 42). 



c^. Color in gray phase light buffy gray nevadensis (p. 44). 



a^. Size medium or small. 



b^. Size very small, hind foot of averaging 26 or less; color buffy gray or brown. 

 Color buffy gray. 



dK Hind foot of c? averaging 26 ocius (p. 107). 



d'^. Hind foot of c? averaging 23 idahoensis (p. 108). 



c^. Color light brown. 



d^. Hind foot of c? averaging 25 myops (p. 130). 



d^. Hind foot of averaging 22 (smallest of the genus) pygmaeus (p. 109). 



