388 U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT 



THOMOMYS, Maxim. 



Thomomys, PBIKCB MAXIM. Nova Acte Acad. C. L. XIX, i. 1839, 383. 



BRAJUDT, Beit. Kcnnt. Saugt. Russlands, 1855. 

 Oryctomys, EYDOCX and GERVAIS, (in part,) Mag. de Zool. VI, 1836, 23. IB. Voy. de la Favorite, v, 1839. 



Anterior face of upper incisors plane or slightly convex, and with a fine groove along the inner margin, sometimes 

 obsolete ; no groove in the centre. Skull not very massive ; zygomata slender. Anterior upper molars with two somewhat 

 divaricated lobes, the anterior considerably smaller and sub-circular. The two middle molars narrowly ami transversely 

 ovate, the acute pointed end outside. Posterior lower molar nearly circular. Fore feet considerably shorter than the 

 hinder ones, comparatively small and weak, with the claws not much developed, though considerably larger than the hinder 

 ones. Second finger and claw nearly equal to the fourth. Cheek pouches moderately large. 



The description of the osteology of Geomys will answer very well for that of Thomomys. The 

 principal differences are seen in the nearly smooth anterior faces of the upper incisors, which 

 have merely a very fine groove along the inner margin and the ovate crowns of the molars, 

 which in Geomys are truly elliptical. 



For the present I leave the species of Thomomys without any attempt to subdivide them, or to 

 exhibit their characteristics in a brief synopsis. All the species of the family vary exceedingly 

 as to color and proportions, especially when these are based on the dried skin. This is exceed 

 ingly extensible, and may thus convey the idea of a comparatively short tail, when, in reality, 

 in nearly or quite all the species, the tail is not much less than half the length of the body. 

 The size of the claws and teeth vary ; the color of the immature, though full grown animal, 

 differs from the adult, and, as already stated, the exact proportions can only be ascertained from 

 fresh specimens, or those preserved in alcohol. The descriptions in the following pages were all 

 made two years ago, and although, with the additional specimens received, a careful revision of 

 the whole subject might have furnished more satisfactory results, yet the time allotted for the 

 completion of the present report will not admit of the necessary delay. I am, however, well 

 satisfied that I have not materially overstated the number of species described, as whatever may 

 be the variations of single specimens from the type, there is an appreciable difference in the 

 series, even though it be difficult of intelligible expression. 



The species to be described are as follows : 



1. Thomomys bulbivorus. Coast of California, from Tejon Pass to some distance north of San 

 Francisco. 



2. Thomomys laliceps. Coast of northern California, (Humboldt Bay.) 



3. Thomomys douglassii. Lower valley of the Columbia River, and Puget's Sound. 



4. ? Thomomys borealis. Upper valleys of the Columbia, towards Rocky Mountains ; proba 

 bly at higher elevations than T. douglassii. 



5. Thomomys rufescens. Upper Missouri and Saskatchewan. 



6. Thomomys talpoides. Shores of Hudson's Bay. 



7. Thomomys umbrinus. Western Texas and New Mexico, along eastern slope of Rocky 

 Mountains, and along the mountains into Sonora. 



8. Thomomys fulvus.Vattey of the Colorado and tributaries, from the San Francisco moun 

 tains to Fort Yuma, and across to San Diego. 



