1888.] MAMMALS FROM TEXAS. 449 



In the skull the most marked ilifference, apart from its smaller 

 size, is in the lesser development of the bullse, and the consequent 

 increase of the space between them, as specially marked by the much 

 greater breadth of the interparietal bones. These latter are very 

 nearly as broad as long, while in all the specimens of D. agilis that 

 I have seen their length is at least double and is often three times 

 their breadth. The muzzle also is rather shorter and slenderer, the 

 front edge of the anterior zygoma-root starts out from it at a sharper 

 angle, and the supraorbital margins are much more nearly parallel to 

 one another, and less divergent posteriorly, tlian they are in D. agilis. 



In all these characters, both cranial and external, D. agilis compactu^ 

 seems to stand on one side of D. agilis typicus exactly where D. 

 deserti, Stephens S does on the other, for just as D. compactus is dis- 

 tinguished by its smaller size, smaller bullse, and broader interparietal, 

 so is D. deserti distinguished by its larger size, larger bullse, and 

 narrower interparietal ; the three forms apparently therefore repre- 

 sent three stages in one single series of development. 



16, Perognathus fasciatus, Wied. 



a-j. d" 2, 12/85 and 4/86. 



Head and Forearm 



body. Tail. Hind foot, and hand. Ear, 



a. cS 96 98 22-2 26-5 6-3 



b. S 99 97 23 26-5 7-0 



c. S 90 90 22-7 26-6 6-1 



d.2 107 104 24-4 29 6-6 



e. 2 99 99 22-9 27 6-5 



/. 2 101 99 23-5 27 6-5 



Mammse 1 — 2=6, 



"These pocket-mice are found all over the county, but indi- 

 viduals are scarce. They remain in their burrows during winter, 

 but live a rather exposed life when grass and weeds cover the ground. 

 They are strong and active, and the ones I had caged were very silent, 

 but made a considerable fuss filling and emptying their pockets. I 

 placed a heap of corn near their nest to see how fast they would 

 remove it ; I think a pair could move a peck one yard in six or seven 

 hours. They appear to fight a good deal, as I often find them with 

 scars and broken tails." — W. T. 



17- Cricetodipus flavus, Bd, 



a-e. 6 2 , 12/85 and 3 & 4/86, 



Head and Forearm and 



body. Tail. Hind foot. hand. Ear. 



a. S 52 50 13-5 160 47 



b. S 51 48 14-2 16-3 5-2 



c. S 52 52 14-1 17 4-4 



d. S 51-5 .52 13-7 16-4 4-5 



1 Am. Nat. xxi. p. 42 (1887). The author unfortunately does not state 

 whether his species has fou or five hind toes. 



