390 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



and western Minnesota (Fort Snelling and Elk Eiver) with, nine 

 skulls of P. sonoriensis nebrascensis from the adjacent plams ot 

 South Dakota, the following differences are found: The skull of 

 P s. nebrascensis is smaller; its zygomatic arches are more nearly 

 parallel to the cranial axis; rostrum relatively shorter, with broader 

 nasals; incisive foramina longer, and the mandible shorter, with 

 a remarkable reduction in the length of its condyloid process, 

 while its coronoid is more developed. Comparing the skulls of the 

 several forms of Peromyscus sonoriensis from the Boundary strip to- 

 gether, the Texas specimens are seen to be considerably the smallest; 

 P. s. sonoriensis is larger; P. s. deserticola and P. s. dementis are decid- 

 edly the largest, deserticola being broader and more massive than 

 dementis; and medius, while smaller than dementis, agrees with it in 

 being narrower and less massive than deserticola. In rufinus the 

 coronoid is most decidedly elongate and uncinate. 



Remarks.— Seven adults of this species, taken in Oklahoma in 

 October and November, are all in the "red" coat, and are much more 

 ochraceous than typical P- s. blandus. They somewhat resemble 

 P. aureolus, as Baird has previously remarked in speaking of certain 

 specimens which he identified as P. texanus. This Oklahoma series, 

 collected by Mr. Jenness Richardson, has been recently sent to me for 

 reexamination by Dr. J. A. Allen from the collection of the American 

 Museum of Natural History, New York. It constitutes a local phase 

 of this species, somewhat intermediate between true P. s. blandus and 

 P. s. nebrascensis, but differing in coloration from either. Peromyscus 

 s. blandus has a decided leaning toward the genus OnycJiomys. Its 

 coloration and the texture of the furry coat are very suggestive of 

 Onychomys. Added to this, it has the coronoid process of the mandi- 

 ble hooked and longer than usual; the posterior pair of tubercles on 

 the soles of its hind feet reduced in size (in Onychomys these are want- 

 ing), and the soles densely furred to the tubercles^. 



Habits and local distribution. — The plains mouse of the Eastern 

 Desert Tract prefers to reside in open country, and the wetter the 

 better. At Dog Spring I caught them in traps set in shallow water; 

 but at Monuments 15 and 40 I found it on rocky hills and buttes, as 

 well as on the level plain. Grassy spots around springs are its fav- 

 orite abodes, and in such places it is abundant. Like Onychomys, 

 it is largely carnivorous, devouring insects or any animal food. It 

 proved to be an annoyance by eating the small mammals caught in 

 our traps, beginning at the abdomen and turning the skin inside out. 

 At Monument No. 46, Mosquito Springs, females were taken May 13 

 and 14, 1892, each containing four large fetuses; and a half-grown 

 young one was taken May 15. 



