RODENTIA—ARVICOLINAE—ARVICOLA. 517 
Arvicota.—C. Prpomys, Baird. 
Ears small, very broad; the anterior edge not inflected. Antitragus well developed into a valve. Feet very broad ; 
anterior about half as long as posterior; claws weaker than in section D, the anterior shortest ; soles with five tubercles 
only ; the tubercles well defined, elevated, as if set in the skin; the posterior very small. Tail, with the hairs, a little less 
than twice the hind feet; about equal to the head. Female with two pairs of teats, only; inguinal. Second upper molar 
with one internal triangle ; third, with one external; anterior lower molar, with two internal and one external closed 
triangles. 
Size large. Hind feet moderate. Toes short. Fore feet about two-thirds as long as the 
hinder, broad, and fossorial. Posterior half of sole hairy. Ears small, concealed, about half 
as long as the hind feet, sparsely furred near the margins. Antitragus very large. Tail a little 
longer than the head, less than one-third the length of head and body. Plumbeous portion of 
the fur becoming darker just before the brown tip. Tail duskier at the tip. 
Skull moderately broad. Interparietal truncate laterally. Nasal branch of interparietal reaching 
considerably beyond the nasal bone to the interorbital region. Second upper molar, with four 
closed triangles, without any spur to the posterior. Third upper molar, with one anterior, one 
external and one internal triangle, with a posterior V. Anterior lower molar, with one posterior, 
two interior, and one exterior triangle, with an anterior lobe or trefoil, with two salient angles 
on each side. Middle lower molar, with five triangles. 
The skull and teeth of A. amphibia resemble this, except that the anterior trefoil has but one 
indentation on each side, lacking the anterior shallow one. A. ratticeps has two lateral triangles 
on each side of the posterior upper molar, instead of one. The lower molars are much like those 
of A. riparia. Arvicola agrestis falls in the group to which A. riparia belongs. 
At present I know of but three species for this section, A. austera, cinnamomea, and haydeni. 
Aryiconra—D. Pirymys, McMurtrie.! 
Ears short ; the anterior margin and concha not inflected. The antitragus scarcely valvular. Fore feet more than two-thirds 
the hinder. Fore claws longest. Hind feet very short, with five tubercles on the soles. The tubercles broad, low, conical, 
apparently like mere elevations of the skin. Tail scarcely longer than the hind feet; considerably shorter than the head. 
Female with only two pairs of teats, in the groin. Second upper molar with one internal triangle ; third with one external ; 
anterior lower molar with two internal and one external closed triangles. 
Size very small; body slender, depressed, closely resembling the shrews in compactness of . 
fur ; fore feet stout, broader than hinder, nearly as long, with longer claws, &c. Ears very 
small, concealed ; the meatus large, with a narrow auricle; rather thinly coated with longish 
hairs. Antitragus very small. Tail very short, considerably less than the head, scarcely 
exceeding the hind feet. 
Skull very broad, width exceeding .60 of the length, convex above. Interparietal acutely 
angular laterally. Nasal branches of intermaxillary longer than the nasal bone, and reaching 
between the orbital spaces. Occipital foramen rounded, as broad as high. Second upper molar 
with four closed triangles, without any spur to the posterior. Third upper molar with only one 
lateral triangle on each side, an anterior triangle and a posterior V. Anterior lower molar, 
with two internal, one external, and one posterior triangle, and an anterior lobe or trefoil, with 
two salient angles on each side. Middle lower molar with four triangles, one lateral triangle 
on each side, the salient angles anterior to those opposite, and forming one triangle. Anterior 
surface of incisors nearly plane ; one-third of lateral surface only covered with enamel. 
The American type of this section is A. pinetorum, of which there appear to be several varieties. 
* Smaller McMurtrie, Am. ed. Cuvier, Regne Animale, I, 1831, 434 ; perhaps equal in part to Microtus, Selys Longchamps 
Etudes de Micromammalogie, 1839, 86. 
