290 PROCEEDINGS OF THE ACADEMY OF 



always observed on the inner side about half way clown the meta- 

 tarsus ; and a similar one is found at the base of each of the 

 diffits. The digits are marked beneath with transverse lines of 

 impression, and end in a smooth slightly clubbed tip. The first 

 disjit, though small, is perfectly formed, and bears an ordinary 

 claw, the tip of which falls opposite the base of the second digit ; 

 the longer 3d digit but slightly exceeds the 2d and 4th, which are 

 about equal to each other ; the end of the claw of the 5th digit 

 falls opposite the middle of the 4th one. 



In the development of the hind limbs of this and the next 

 closely allied species of Perognathus, there is more indication of 

 a saltatorial tendency than appears in the case of P.fasciatus, 

 but the difference is not very striking; it is no more than that 

 which may be inferred on comparison of Cricetodipus parvus 

 with C. flavus, and it falls far short of the state of the case exhi- 

 bited by Dipodomys. Still, the supposed saltatorial character is 

 further borne out, upon analog3 r , by the peculiar character of the 

 long penicillate tail, already fully described. 



I find it difficult to describe the color of the upper parts satis- 

 factorily. It has been called " a light dull yellowish-brown or 

 tawney, lined with dark-brown." The prevailing tone is decidedly 

 " gray" in comparison with the strong mixed yellowish and black- 

 ish of P. fasciatus somewhat the shade of dilute coffee and milk. 

 The lighter hairs are dull yellowish-gray, with darker lining of 

 hair brown. There is a general tinge of the palest possible cinnamon. 

 All the bases of the hairs are of the color of fresh-cut lead. 

 There is no appreciable lateral stripe of different color from the 

 upper parts, although just along the line of junction with the 

 white, the color lightens a little for lack of the darker brown 

 lining. The extreme tip of the snout, the cheeks, the whole fore 

 leg, the inner aspect of the hind leg, the feet, under side of tail, 

 and under parts generally, are white; the line of demarcation 

 runs straight from nose to hind leg, where it drops down to the 

 heel. The upper surface of the tail and the brush at the end are 

 hair-brown. Some of the whiskers are black; others, like the 

 claws, are colorless. 



The external sexual characters of this and other species of the 

 family are readily recognizable. In consequence of the develop- 

 ment of the os penis, the preputial sheath is a resisting prominence 



