6 Bailey Identity of Thomomys umbrinus (Richardson). 



the most accessible localities in Southern Mexico from which 

 any species of Thomomys is known. 



The following description is based on 8 specimens from Boca 

 del Monte, Vera Cruz, Mexico: 



Thotnomys umbrinus (Richardson). 



Geomys umbrinus Eichardson. Fauna Boreali-Americana, I, pp. 190 and 

 202, 1829. 



General characters. Size medium, hind foot 27 to 28 ; colors dichromatic, 

 dull umber brown or plumbeous black ; skull short and wide with strongly 

 projecting incisors. 



Color. Upperparts, in brown phase, dull burnt umber or Prouts brown, 

 varying to nearly black in some specimens; lowerparts lightly washed 

 with pale buffer whitish, in some specimens sharply contrasted with dark 

 upperparts ; feet, tip of tail, chin, and sometimes throat, white. In black 

 phase slaty black all over except white chin, feet, and tip of tail. 



Skull. Short and wide with incisors projecting well beyond nasals ; angle 

 of frontal projecting into notched anterior base of zygoma ; lachrymal 

 applied for nearly its whole length to zygoma ; premaxillee of approximately 

 the same length as nasals and widest near blunt posterior tips ; incisors 

 slender, in comparison with those offalvus; color of incisors varying from 

 light yellow to dark orange. 



Measurements. Average of seven adults from Boca del Monte: Total 

 length, 193; tail vertebrae, 58; hind foot, 27. Skull, No. 64,091, cT, from 

 Boca del Monte : Greatest length, 36 ; diastema, 13.5 ; front of occiput to tip 

 of nasals, 33 ; nasals, 12.5 ; interorbital constriction, 6.4 ; zygomatic breadth, 

 24 ; alveolar length of upper molar series, 7.5. 



