146 Merriam New Mammals from Southern Mexico. 



Thomomys peregrinus sp. nov. 



WANDERING THOMOMYS. 



Type from SALAZAR, STATE OF MEXICO. No. 50130 9 yg-' a d. United 

 States National Museum, Department of Agriculture Collection. Collected 

 October 23, 181)2, by E. W. Nelson (original number, 3668). 



Measurements (taken in flesh.) Type specimen : Total length, 207 ; tail 

 vertebrae, 72 ; hind foot, 28.5. Average measurements of 10 specimens 

 from type locality : Total length, 201 ; tail vertebrae, 57 ; hind foot, 28. 



General Characters. Similar to T. fidvus, but much darker and 

 duller, lacking the bright golden-fulvous tints of that species, 

 and differing also in cranial characters. The incisors curve far 

 forward. 



Color. Upper parts dark^ umber-brown, becoming sooty-black 

 on head and along middle of back, and dull fulvous on sides ; 

 end of nose, broad ring round mouth, and ear-patches blackish ; 

 under parts huffy, the plumbeous basal fur showing through ; 

 toes of fore feet, most of hind feet, and distal i or } of tail 

 white. On the hind feet the dark color of upper parts reaches 

 down over ankles ; on fore feet it usually comes down to or near 

 bases of toes. 



Cranial Characters. Compared with T. orizabse, the muzzle is 

 very narrow, the breadth across ascending branches of premax- 

 illaB being much less than the interorbital breadth. The frontals 

 anteriorly are also considerably narrower than interorbitally, 

 and the premaxillas are slender and pointed posteriorly. In 

 young and middle-aged skulls the interparietal is straight pos- 

 teriorly, broadly rounded anteriorly, and nearly twice as broad 

 as long ; in old skulls it is roughly subquadrate. 



