1895.] NATURAL SCIENCES OF PHILADELPHIA. 37 



have been compared with a series of fulvus loaned by the American 

 Museum of Natural History through the courtesy of Dr. J. A. 

 Allen. Specimens of same age and season from southern Arizona 

 show that the San Diego County animal is uniformly blacker and less 

 fulvous, but the close resemblance in cranial characters of the two 

 series will not justify their separation as full species. Two specimens 

 from the San Jacinto and Cuyamaca Mountains, respectively, taken 

 at altitudes of five to six thousand feet, are ideutical with those from 

 Witch Creek. 



Note on Thomomys perpallidus. 



A large series of beautifully prepared specimens of T. perpalli- 

 dus have incidentally been examined in my studies of the southern 

 California forms. The cranial characters of these specimens com- 

 pared with those of fulvus of similar age and size, show considerable 

 agreement. Of these may be specially noted the broad interparietal, 

 wide, heavy incisors and molars, and the slenderness of the bones of 

 the zygomatic arch. Correlated with their cranial likeness it may 

 be noted that darker summer specimens of perpallidus form a close 

 intergrade of color with lighter examples of fulvus, connecting, in an 

 unexpected manner, the extreme light phase of the former with the 

 darker phase of the latter species. Not having specimens from any 

 locality between Agua Caliente, California, and the San Francisco 

 Mts., Arizona, I am unable to do more than conjecture whether an 

 uninterrupted series would not justify naming the Mojave Desert 

 Gopher Thomomys fulvus perpallidus. So far as the evidence goes, 

 however, the relationship of the two animals is quite close. 



Through the kindness of Dr. J. A. Allen, I was able to secure a 

 loan from the American Museum of Natural History of typical speci- 

 mens of several species of Thomomys from upper and Lower Cali- 

 fornia and Arizona, without which the conclusions arrived at in this 

 paper would have been of little value. 



