MURIDAI—SIGMODONTES—NEOTOMA. 7 
of the typical genus Mus,—not being indigenous to this country, and being, 
moreover, among the best-known of mammals, will not be treated in the 
present paper. 
Tribe SIGMODONTES. 
Under this head come all the Murine indigenous to America. Those 
of the northern division of the hemisphere may be grouped under four 
genera,—Neotoma, Sigmodon, Ochetodon, and Hesperomys; the latter with 
three subgenera. Full descriptions of these and of their respective species 
follow. 
Grnus. NEOTOMA, Say & Ord. 
Mus, sp., Say & Orb, 1818-23.—DesMaresT, 1822. 
Arvicola, sp., HARLAN, 1825. 
Lemmus, sp., FISCHER, 1829. 
Neotoma, SAY & Orn, Journ. Acad. Nat. Sci. Phila. iv, pt. ii, 1825, 346 (type, NV. floridana).—Aup. & Bact, 
- Quad. N. A. i, 1849, 31.—Bairp, M. N. A. 1857, 486.—Cours, Proc. Acad. Nat. Sci. Phila 
1875, 174. 
Myoxus, sp., RICHARDSON, Zool. Journ. iii, 1828, 517 (N. cinerea). 
Teonoma, J. E. Gray, Proc. Zodl. Soc. Lond. 18—, p. — CX. cinerea). 
Cuars.—Embracing sigmodont rats of the largest size; highly murine 
in general aspect; peculiar to North and Middle America. Snout pointed, 
mobile; whiskers very long (the longest ones reaching to or beyond the 
shoulders) ; eyes large and full (as in Dipodomys) ; ears very large, orbicular, 
nearly naked. Tail long, nearly equaling the body with or without the head, 
either scant-haired (nearly as naked and scaly as in Mus) or bushy (much as 
in Myozrus). Feet small, but broad for their length, with short toes; the fore 
with four perfect clawed digits, which in length run 3d; 4th, 2d, 5th; and a 
rudimentary thumb bearing an abortive nail; the hind with five perfect 
clawed digits, the middle three of which are subequal and longest ; the 5th is 
not much shorter, its claw reaching about to the base of the 4th claw, while the 
1st reaches about to the median node of the 2d. Palms naked, 5-tuberculate ; 
one tubercle postero-external, another postero-internal near base of pollex ; 
two at bases of 2d and 5th digits, respectively, and one at base of 3d and 4th 
digits together. Soles naked at least for their anterior two-thirds—the pos- 
terior third hairy in northern species, mostly naked in tropical forms; fur- 
nished with seven tubercles, thus: one near postero-external angle of foot, 
only evident in naked-soled species ;* a larger one a little farther in advance 
over which the skin is not particularly thickened. 
