MURID.E— ARVICOLIN^— ARVIOOLA. 151 



toimjs). 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 (cf. Synaptomys). 

 Under incisor roots running past the last molar, and thence up tin 1 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 (cf. 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 (cf. 

 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 fossae leading directly out to the 

 pterygoids. Incisive, foramina short and close, attaining neither incisors nor 

 molars, but midway between both. Nasals anteriorly subtruncate opposite 

 incisive 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 papillae; 

 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 £-§ 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 entirely 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, 



