M UR1DM— SIGMODONTES— ORYZOM YS. 1 1 1 



(perhaps a little stretched), 3.75; tail to end of vertebrae, 1.90; to end of 

 hairs, 2.00; fore foot, 0.40; hind foot, 0.80; ear 0.70 high, 0.40 wide. 

 Camp Grant, Arizona. The specimen is a female, apparently having recently 

 bred, showing four well-developed inguinal teats ; pectoral mammae, if existing, 

 have eluded our search, and were certainly not functionally developed in 

 this case. 



As already intimated, this single specimen is differentiated from leuco- 

 gaster according to extensively applicable laws of geographical variation ; for 

 which reason we suspect that intermediate examples will eventually be found, 

 showing it to be merely an offset from leucogaster. But if any links exist, 

 they remain unknown. 



Subgenus ORYZOMYS, Baird. 



< Mus sp. Haplan, Am. Journ. Sci. 1837 



< Hesperomijs sp. Wagner, Suppl. Schreb. 1843. 

 X An-icola sp. Aud. & Bach., Q. N. A. iii, 1853. 



= Orywmys, Baird, M. N. A. 1857, 458 ; type, Mus palustris, Hael. 

 Coues, Proe. Acad. Nat. Sci. Phila. 1874, 183. 



Chars. — Superior margin of orbit with a prominent sharp edge or bead. 

 Anteorbital foramen nearly circular above (somewhat as in Zapodidce), con- 

 tinued below as a slit much narrower than in Hesperomys proper. Maxillary 

 plate forming outer wall of the foramen not produced anteriorly into a pointed 

 process (cf. Sigmodon). Posterior border of palate produced behind last 

 molars, a deep pit intervening on either side ; post-palatal notch narrow, with 

 parallel sides, and nearly straight, transverse, anterior border. Hind legs short, 

 but feet very long and large (much as in Fiber), with obliquely-set long toes ; 

 densely pilous above, but soles perfectly naked, granular, with one long, nar- 

 row, poslero-internal tubercle (as in Mus) and five small ones. Lateral toes 

 very unequal in length, the fifth reaching to the penultimate joint of the fourth 

 (cf. Sigmodon^ ; all the toes have a slight but evident basal webbing. Fore 

 feet small, not half as long as the hinder, pilous above ; palms perfectly naked. 

 Ears small, little overtopping the fur, hirsute both sides, with a fluffy tuft on 

 the concavity. Nasal pads more noticeable than in other sections. Tail 

 long, about equaling head and body, scant-haired, especially above where the 

 dermal scales as well as the vertebral annuli are visible. Fur glossy, but 

 coarse from the number of bristly hairs. AVhiskers sparse and short, exceed- 



