MURID4—ARVICOLINA—ARVICOLA. 151 
tomys). Anterior lower molar of 5 to 8 prisms, of which the anterior forms 
an irregular treffle, the posterior a transverse loop, the intermediate forming 
lateral, alternating. closed triangles; this molar nearly as long as the other two 
together. Middle lower molar of 4 to 5 prisms, of which the last forms a 
transverse loop, the rest forming alternating lateral triangles (cf. Evotomys). 
Posterior lower molar abruptly narrower than the rest, never of more than 3 
prisms (cf. Synaptomys, Myodes) seriatim, each making a transverse loop (no 
lateral or alternating triangles). Upper incisors plane (ef. Synaptomys). 
Under incisor roots running past the last molar, and thence up the back of 
the condylar process, forming a thickening of the ramus, or a strong ridge 
that subsides at the notch between condyle and descending process (ef. Synap- 
tomys, Myodes). Skull solid, massive, its zygomatic diameter slightly exceeding 
its length; interorbital constriction abrupt; temporals angularly encroaching 
on orbits Zygomata not dipping to level of palate, slightly expanded. Pos- 
terior termination of bony palate never a single, abrupt, transverse shelf (ef. 
Evotomys, Myodes, Synaptomys), but palate ending between ultimate molars 
by dipping to a conspicuous fossa on either side, between which is the narrow 
median fissure of the posterior nares; said fossee leading directly out to the 
pterygoids. Incisive foramina short and close, attaining neither incisors nor 
molars, but midway between both. Nasals anteriorly subtruncate opposite 
incistve alveoli; posteriorly subequal or equal to nasal branches of maxillary, 
which reach nearly or quite to orbits. Coronoid process rising as high as the 
condyle (cf. Evotomys). Size medium for the subfamily ; form stout; mem- 
bers short, but none of them rudimentary; neck indistinguishable; head 
broad, with convex forehead; muzzle obtuse ; lip fairly cleft, hirsute; eyes 
small, midway between ears and snout; muzzle furry, except nasal papille ; 
whiskers 5-seriate. Ears well developed (cf. Myodes), but never noticeably 
overtopping the fur, orbicular, more or less hirsute both sides, with valvular 
antitragus. Fore feet 5-3 the hind feet, with mostly naked tuberculate palms, 
4-digitate; thumb obsolete, with abortive, obtuse, flattened, sessile nail; fin- 
gers unguiculate, inferiorly scutellate. Hind feet with soles neither entirely 
naked nor entircly furry, 5-G-tuberculate, the posterior tubercle long, 
5-digitate; three middle toes longest and subequal, 5th and 1st successively 
much shorter. Tail terete, always hairy enough to obscure or conceal its 
annuli, and with terminal pencil, sometimes densely hirsute; always longer 
than the sole, generally exceeding the head, but ranging in length from about 
