142 
of the surrounding sheets of enamel that meet from opposite sides and 
fuse along the median line; upper molars sub-equal in length and | 
breadth; anterior lower molar nearly as long as the other two together. 
Skull solid, massive. Size medium for the sub-family; form stout ; mem- 
bers short; neck indistinguishable; head bread, with convex forehead ; 
muzzle obtuse; lips fairly cleft, hirsute; eyes small, midway between ears 
and snout; muzzle furry, except nasal papille; whiskers 65-seriate; 
ears well developed, net usually overtopping the fur, orbicular, more or 
less hirsute both sides, with valvular antitragus; fore feet with mostly 
naked, tuberculate palms, 4 digitate; thumb obsolete, with abortive, 
obtuse, flattened, sessile nail; fingers unguiculate, inferiorly scutellate ; 
hind feet with soles neither entirely naked nor entirely furry, 5 to 6 tuber- 
culate, 5-digitate; three middle toes longest-.and sub-equal, fifth and first 
successively much shorter; tail terete, always hairy enough to obscure 
its annuli, and with terminal pencil, sometimes densely hirsute, always 
longer than the sole, usually longer than the head, but ranging in length 
from as long as head to nearly half as long as trunk; pelage thick, soft, of 
ordinary fur mingled with longer bristly hairs; fur uniformly plumbeous 
at the roots, colored at the tips; general color subdued, the shades diffuse, 
under parts lighter than upper, tai! bicolor. 
Four groups of Arvicola are recognized by Professor Baird, and charac- 
terized by Dr. Coues on dental and external characters: A—Myonomes, 
B—Chilotus, C—Pedomys, and D-=Pitymys. 
t 
SuB-GENUsS Pepomys Baird. 
Pedomys, Baird, M. N. A., 1857, 517 (type, Arvicola atisterus, LeConte).— 
Coues, Proc. Acad. Nat. Science, Phila., 1874, 190. 
Sub-generic Characters —Back upper molar with one external triangle 
and a posterior trefoil; middle upper molar with one internal triangle; 
front lower molar with one external and two internal triangles; ear un- 
rimmed; sole 5-tuberculate; fore claws not larger than hinder ones; tail 
about one-third length of head and body, or a little less; pelage ordinary, 
grizzly, and rather “austere,” the under parts usually with a peculiar, 
muddy tinge. 
The above section is based, By Baird, on A. austerus, LeConte. The 
same author added to the group two other species—-A. haydent and A. 
cinnamomeus—neither of which are regarded by Dr. Coues as specifically 
distinct, 
