15 



Hah. Interior of United States, between Mississippi and Rocky 

 Mountains. Upper Missouri. Red River of the North {Coves). 

 W\'oniing. Kansas. Doubtless of more extended, but as yet un- 

 ascertained range. 

 8. Hesperomys (Onychomys) torridus, Coues. 



Diag. Resembling O.leucogaster ; tail longer, ears larger, soles 

 less hair}', fore claws weaker. Coloration much more yellowish ; 

 no darker dorsal area ; snout, feet, and all under parts tawny- 

 white ; dusk}' stripe on top of tail ver}' narrow, not reaching the 

 tip. Length of head and body 3.75; of tail 2.00; of forefoot 

 0.40 ; hind foot 0.80 ; ear about 0.75 above notch. Onl}- two pair 

 (inguinal) of teats discovered. (Type No. 9886, Mus. S. I.) 



Hab. Arizona. 



Subgenus Ortzomts, Baird. 

 Syx. Mus, sp., Harl., Am. Journ. Sci. 1837. — Hesperomys, sp., "Wagn. 

 Suppl. Schreber, 1843, and authors. — Arvicola, A.\\A. & Bach., Q. N. 

 A. iii. 1853. — Oryzomys (subg.), Bd., M. N. A. 1857, 458 (type Mus 

 palustris, Harl.). 



Char. Orbits beaded. Anteorbital foramen nearly circular 

 above (somewhat as in Jaculus) continued slit-wise lielow, wliere 

 narrower than in Vesperivius ; the maxillary plate bounding it 

 not produced into a pointed process (compare Signiodon.) Palate 

 produced behind last molars — a deep pit on either hand. Coro- 

 noid attaining level of condyle. Hind legs short, but feet very 

 large, with obliquely set toes (much as in Fiber) in evident adap- 

 tation to aquatic habits. Soles perfectly naked, granular, with 

 one long, narrow, postero-internal tubercle (as in 3Ius and five 

 small ones. Toes with evident basal webbing ; very unequal in 

 length, the fifth reaching to the penultimate joint of the fourth 

 (compare Sigmodon). Fore feet not half as long as the hinder ; 

 palms perfectly naked. Ears small, little overtopping the fur, 

 hairy both sides, with a fluffy tuft in the concavity. Nasal pads 

 more evident than in other sections. Tail long, about equalling 

 tlie head and body, scant haired ; tlie dermal scales and vertebral 

 rings evident. Fur glossy, but coarse and hispid. Larger than 

 diUy other N. American species of Hesperomys ; general aspect of 

 Sigmodon or even Mus proper. 



