NATURAL SCIENCES OF PHILADELPHIA. 



283 



Exj)lanation of figs. Left ear, 

 in each case, twice natural 

 size; upper fig. P. monttcola; 

 middle fig. P. penicillatus ; 

 lower fig. Cricetodipus fla- 

 vus. 



There appears to be something peculiar, 

 in the habits perhaps, rather than in the 

 scarcity, of the species, which prevents the 

 acquisition of large series of specimens in 

 this family. While hundreds of examples 

 of animals no larger or more conspicuous 

 than these are readily amassed, collections 

 are all deficient in Perognathus and Crice- 

 todipus, and not very full in Dipodomys. 

 I have not been able to examine more than 

 a hundred specimens altogether, and of 

 these more than half were Dipodomys. Of 

 Perognathus I have however specimens of 

 all the described North American species, 

 including all of Baird's types and consider- 

 able additional material. After protracted 

 examination, I endorse the validity of all 

 the species admitted by that author in 

 1857, and find indications of the probable 

 existence of one or two more. This point 

 is fully discussed beyond. The species 

 that appear to be established may be readily 

 determined by the following analysis, viz: 



A. Notch of the ear bounded in front by a slight, 

 though distinct, lobe of the tragus. Whole 

 fore leg white. 

 a. Tail penicillate, crested at the eud, rather 

 longer than the body and head. Sides with no fulvous stripe. 



PENICILLATUS. 



b. Tail simple; sides with a strong fulvous stripe. 



1. Tail decidedly shorter than the body and head. Length about 4 

 inches. Pelage moderately stiff. Mixed sandy and blackish. 



FASCIATUS. 



2. Tail not shorter than head and body. Length about 3 inches. 

 Pelage very hispid. Mixed cinnamon and blackish. . . hispidus. 



B. Notch of ear formed in front directly by the edge of the conch. Fore 

 leg mostly colored like the back. 



Tail simple ; lateral stripe obscure monticola. 



Perognathus fasciatus, Maxim. 



Perognathus fasciatus, Maxim., N. Act. Akad. Leop-Caes. Nat. Cur. xix. 

 pt. i. 1839, 369, pi. 34 ; Reise Nord-Am. i. 1839, 449 ; Arch. f. Na- 

 turg. 1861, ; Verz. Reise, 1862, 175, pi. 4, f. 6, 7. Wagn., Arch. 



