NATURAL SCIENCES OF PHILADELPHIA. lS3 



Hah. Interior of United States, between Mississippi and Kock}" 

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

 Wyoming. Kansas. Doubtless of more extended, but as yet un- 

 ascertained range. 



S. Hesperomys (Onychomys) torridus, Coues. 



Diag. Resembling O.leucogaste?' ; tail longer, ears larger, soles 

 less hairj', fore claws weaker. Coloration luucli 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 3.15 ; of tail 2.00 ; of fore foot 

 0.40; hind foot 0.80 ; ear about 0.75 above notch. Only two pair 

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



Hab. Arizona. ' 



Subgenus Obyzomys, Baird. 



Syn. 3fus, sp., Harl., Am. Journ. Sci. 18^7. Hesperomi/s, sp., Wagn. , 

 Suppl. Schreber, 1843, and authors. Arvicola, Aud. & Bach., Q. N. 

 A. ill. IQrid.Onjzomy.^ (suljg.), Bd., M. N. A. 1857, 458 (type 3Iuh 

 2?ttlustri><, Harl.). 



Char. Orbits beaded. Anteorbital foramen nearly circular 

 above (somewhat as in Jaculua) continued slit-wise below, where 

 narrower than in VesperimuH ; the maxillary plate bounding it 

 not produced into a pointed process (compare Sigmodon.) 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 wnth 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 flufty tuft in the concavity. Nasal pads 

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

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

 rings evident. Fur glossj', but coarse and hispid. Larger than 

 any other N. American species of Hesyeromys ; general aspect of 

 Sigmodon or even 3Ii(s i)roper. 



