L893.] NATURAL SCIENCES OF PHILADELPHIA. 411 



ashy upper fourth of tail extending to tip; a faint streak of brownish- 

 black on under side of middle third of tail disappearing toward either 

 extremity. Soles scarcely darker than white feet. Tail strongly 

 crested-penicillate, the vertebra- one and one- half times as long a s 

 head and body. General shade of upper parts slightly darker than in 

 deserU, inclining to cinnamon on rump in adults. 



Measurements. — Total length, 241 ; tail vertebrae, 149; pencil, 35; 

 hind foot, 38 ; ear from crown (dry) !t. Skull — Basilar length, 

 21-8; mastoid breadth, 24 ; inteorbital constriction, 14-5; length 

 of nasals, 13; length of mandible to base of incisor, 13*8; height 

 of coronoid process from angle, o-6. 



Six specimens were taken, all in the Mohave Desert at Agua 

 ( 'aliente. The average measurements are less than those given 

 above. This species is easily distinguishable from desert i by small 

 size, slightly darker coloration and lack of white tip to tail ; from 

 similis by its lack of black on rump, tail, soles and hind legs. 



.">. Dipodomys similis, sp. aov. (Type No. 1017. 9 ( '"'- Acad. Nat. Sciences, 

 Phila.: White Water. San Diego Co., California, Oct. 24. 1803. col. by R. B- 

 Hefron). 



Description. — In size and color pattern almost an exact counter- 

 part of Perodipus agilis. Colors similar to D. simiolus and D. 

 deserti but darker than either and with tail and limbs relatively 

 shorter than the latter. Above light tawny tipped and lined 

 sparingly with blackish, the latter color more pronounced on rump. 

 Posterior surface of thigh to heel, soles, ring around eyes, base of 

 whiskers, top of nose and upper and lower fourths of tail to tip, 

 blackish. The remainder of body white, including small spot above 

 eye, a larger one at posterior base of ears and stripe across thighs. 

 Ears grayish. Tail crested-penicillate. 



Measurements. — Total length, 241; tail vertebra', 148: pencil, 

 2-1; hind foot, 38 , ear (dry) above crown, 10 - o. Skull — -basilar 

 length, 22; mastoid breadth, 24*5; interorbital constriction 14; 

 length of nasals, 14: height of coronoid process from angle, 5. Skull 

 similar to that of simiol lis but with smaller mastoids and wider across 

 ante-orbital processes of maxillary. In similis the lower premolar is 

 narrower anteriorly than posteriorly and as long as wide, in simiolus 

 it is of equal width on both faces and much wider than long. In 

 similis the extremity of angle of mandible is prolonged and acum- 

 inate, in simiolus it is shorter and rounded at the extremity. 



