RODENTIA GEOMYINAE THOMOMYS UMBRINUS. 401 



The specimens No. 154, 149, agree very well with each other, the colors of the latter and 

 8 maller one being brightest. 



A specimen (611) collected by Dr. Henry, probably at the Copper Mines, agrees in all essential 

 characters,, except that the furrow of the incisors is a little more distinct, and the reddish of 

 the under parts is a little more mixed with paler. Another of much larger size, (612,) appears 

 bleached ; the under parts being much paler than as above described. The body measures 

 nearly eight inches. The tail is, unfortunately, mutilated, by having been broken off near the 

 base ; the wound is, however, cicatrized. This mutilation of the tail is very common among 

 the species of Geomys, rendering it difficult to apply the proportional length of this member as 

 a specific character. It is probable that this result is produced in the course of the contests in 

 which male mammals periodically indulge. 



This species, in general appearance, has a close resemblance to T. bulbivorus, from the Pacific 

 coast, though a careful comparison shows many points of difference, which, though, slight, are 

 as characteristic as generally prevails in this group. The claws are uniformly longer, stouter, 

 and considerably more curved. The toes, however, are shorter, as well as the hind feet. The 

 tail is rather longer, and in most cases is uniformly dusky all round, above and below, except 

 the terminal third or fourth, while in T. bulbivorus the tail is grayish white with a dusky line 

 running to a point on the upper half from the base. T. bulbivorus exhibits no wash of very 

 dark reddish brown on the back, but is finely mottled with dusky, almost the same on the sides 

 and flanks as on the back ; instead of having the latter decidedly lighter, clearer, and more 

 uniform than the back. The groove on the inner edge of the upper incisor is rather obsolete 

 in both, most distinct in T. bulbivorus. I do not find any appreciable difference in the skulls, 

 except what may naturally arise from the comparison of unequal ages. 



In this species I am inclined to recognize the long lost Geomys umbrinus of Kichardson, 

 received by Leadbeater from the "town of Cadadaiguos, in the southwestern part of Louisiana." 

 I have not been able to find this locality mentioned anywhere in North America, not to mention 

 Louisiana ; it may be some obscure locality in Texas, Arkansas, or New Mexico, known at the 

 date of its reception by Leadbeater, (prior to 1829,) but since forgotten. There are some differ 

 ences from the description to be noticed in most of the specimens. Thus I do not find that the 

 fur has the "lustre and appearance of that of the muskrat ;" nor are the sides of the mouth 

 dark brown, the chin and throat white, as described in Geomys umbrinus. On the contrary, 

 the chin is sooty black or brown, the throat and under parts usually chestnut. Still, Richard 

 son's specimen may have presented these variations from the type, and I do not feel willing to 

 run the risk of encumbering science with another synonym by proposing a new name without 

 further opportunities of investigation. 



G. umbrinus is described as having smooth upper incisors, but I know of no species entirely 

 devoid of a furrow, though this may be very obsolete, as is the case with the specimens before me. 



51 L 



