44 POCKET GOPHERS OF THE UNITED STATES. 



soft, loose sand, their holes might be easily broken into by predatory 

 animals or washed open by rain but that the precaution is taken to pack 

 them full of sand for a distance of 3 to 6 feet from the opening where 

 the dirt is thrown out. Usually their burrows can not go very deep 

 without reaching water, which was found standing in some of them. 

 In no case did I find more than one Gopher in a burrow. They live in 

 colonies, which are often a mile or more apart." 



habits of baird's gopher ( Cratogeomys castanops}. 



This Gopher lives on the western part of the Great Plains south of 

 the latitude of Las Animas, Colo. J have observed it in but one 

 locality, Sierra Blanca, Tex., where it was living on the dry, gravelly 

 mesa amid such desert plants as cactuses, mesquites, acacias, and 

 yuccas. A preference for dry uplands appears to be characteristic of 

 this species, as is further shown by the observations of Dr. A. K. Fisher, 

 who furnishes the following note: " Geomys castanops and Geomys 

 lutescens are about equally common at Las Animas, near Old Fort 

 Lyon, Colo. The latter species is found mainly in the alfalfa fields, 

 where the ground is kept wet by irrigation, though at least one speci- 

 men was taken in dry soil in close proximity to the other species. G. 

 castanops, on the contrary, inhabits the dry, sandy mounds not reached 

 by irrigation, and is most common in waste ground grown up with sun- 

 flowers, near railroads, and along the higher banks above the grassy 

 bottoms bordering Purgatory Creek. They were difficult to capture 

 on accouut of the dryness and looseness of the soil and consequent 

 caving in of the burrows, caused by walking near where the traps 

 were set. Six specimens were secured July 16-17, 1892." 



habits of the GRAY pocket gopher (Thomomys talpoides). 



(Plate I.) 



This species may be distinguished from the Prairie and Plains 

 Gophers — the only species coming near it geographically — by smaller 

 size, grayer color, slenderer form, and in all ages and conditions by the 

 smooth front face of the upper incisors, which in Geomys are deeply 

 grooved lengthwise. 



The two animals are not known to occur in the same localities except 

 along the eastern part of South Dakota and southeastern North Dakota, 

 in which region their ranges meet and slightly overlap. Both have 

 been taken at Portland, Traill County, and Valley City, Cass County, 

 K Dak.; and at Fort Sisseton, Marshall County, S. Dak. Why the 

 two should not intermingle while separated by no apparent barrier is 

 an unsolved problem in distribution. The separation does not appear 

 to occur along any zonal line and can not be accounted for by differ- 

 ence in latitude, altitude, or humidity. Usually where their ranges 

 meet there is a neutral strij) between in which few, or none, of either 

 occur. There are two possible solutions of the problem: Soil, and 



