22 



NOETH AMERICAN FAUNA. 



[no. 39. 



as to be considered partially melanistic. There are two black skins of 

 T. talpoides from Red Deer, Alberta; one of T. rufescens from Fish Lake, 

 in the Turtle Mountains, N. Dak. ; one of T. fulvus from Trumbull 

 Mountains, Ariz.; one of T. toltecus from Fairbanks, Ariz.; and several 

 specimens of T. hottx from widely separated localities in California. 

 This is by no means an exhaustive list of melanistic specimens, but 

 merely serves to show how common and widely represented is this 

 variant phase. 



Abnormal marking of another type is undoubtedly caused by tick 

 bites. In many specimens of T. fossor from the mountains of Colo- 

 rado, Wyoming, and New Mexico small white specks occur scattered 

 irregularly over the top of head and shoulders, giving the animal a 

 speckled appearance similar to that of tick-bitten Texas horses. The 

 fact that these occur only on the parts of the gophers' bodies not to 

 be reached by their teeth strongly suggests as their origin the pres- 

 ence of small ticks which engorge and remain attached to the skin 

 long enough to produce sores, which when healed are covered with 

 white instead of normal hair. Gophers with speckled heads are 

 represented from Colorado by specimens from 3 and 7 miles east of 

 Cochetopa Pass, from Hahns Peak, Rabbit Ear Mountains, Elk Head 

 Mountains, Longs Peak, Estes Park, Baxter Pass, and Pearl; from 

 Wyoming, by a specimen from Bridger Peak; from Utah, by speci- 

 mens from the Beaver Mountains; and from New Mexico, by specimens 

 from Costilla Pass, Costilla River (near source), Red River (near 

 source), Taos Mountains, and Twining. 



A somewhat similar abnormal condition is found in a few speci- 

 mens of T. fuscus from northwestern Montana. The top of the head 

 and shoulders becomes gray from a considerable mixture of white 

 hairs. The hair has a thin and unnatural appearance, the result, it 

 has been suggested, of mange or a similar skin disease. 



VARIATION AND DISTRIBUTION. 



The great variety of slight characters and lack of more trenchant 

 characters over a wide range, the abundance and almost continuous 

 dispersal of the genus in this range, and the evident uniform vigor 

 of the whole group indicate that the genus is at the height of its 

 development. It has pushed out from the other perhaps older, more 

 widely differentiated genera of the Geomyidse and covered more ter- 

 ritory and produced more species and subspecies than all the rest of 

 the family. In 1895 . Dr. Merriam recognized in the Geomyidse, ex- 

 clusive of TJiomomys, 8 genera embracing 37 species. The genus 

 Thomomys, without even a valid subgenus,^ contains at least 88 

 recognizable forms of 40 species, and occupies about twice the area 

 of the rest of the family. (See figs. 5 to 10.) 



1 See first footnote, p. 17. 



