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 broad, with convex forehead ; 

 muzzle obtuse ; lips fairly cleft, hirsute ; eyes small, midway between ears 

 and snout; muede furry, except nasal papillee; whiskers 5-seriate; 

 ears well developed, not 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, 6 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 terndinal 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 difiuse, 

 under parts lighter than upper, tail bicolor. 



Four groups of Arvieola are recognized by Professor Baird, and charac- 

 terized by Dr. Coues on dental and external characters ; A — MyonomeSy 

 'B—Chilotm, C — Pedomys, and D—Pitymys. 



Subgenus Pedomys Baird. 



Pedomys, Baird, M, N. A., 1867, 517 (type, Arvieola aitsterusy 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 6-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. haydeni and A. 

 nnnamomeus — neither of which are regarded by Dr. Couee as specifically 

 distinct. 



