46 Zoology of Colorado 



of consobrinus overlaps that of operarius. Anyone who happens 

 to be in these regions of overlapping range should look out for 

 possible hybrids. 



The Geomyidae or pocket gophers are digging animals with 

 stout limbs, the cheeks with well-developed external pouches. 

 The tail is short and the ears are small. We have in Colorado 

 three genera, Thomomys* in which the upper incisor teeth are 

 quite smooth or with a minute groove near the inner edge; Cra- 

 togeomys, in which these teeth have a distinct longitudinal groove, 

 and Geomys (the name meaning earth-mouse) in which there are 

 two such grooves. Eight kinds of Thomomys have been found 

 in Colorado. The larger forms, over eight and one-half inches 

 long, are T. fulvus of Woodhouse, dark, tawny or dull chestnut; 

 T. fulvus pervagus of Merriam, larger and paler; T. perpallius 

 aureus of Allen, golden buff; T. perpallidus apache of Bailey, 

 dark, with hind feet and tip of tail conspicuously white. The 

 last, not mentioned in Warren's book, was found at Arboles and 

 Bayfield. All these have the mammae in four pairs. The 

 smaller forms, less than eight and one-half inches, are T. ocius 

 of Merriam, color very pale, mammae normally in seven pairs; 

 T. fossor of Allen, dull and dark brown, with rather large ears, 

 mammae in five pairs; T. talpoides clusius of Coues, paler than 

 fossor, more buffy brown, mammae in six or seven pairs; T. 

 talpoides agrestis of Merriam, larger and paler than the last. 

 There is considerable seasonal and individual variation in color 

 which makes the identification of the animals difficult without 

 close study. The common species in the mountains is T. fossor, 

 which goes up to and above timber line. T. clusius is found 

 along the eastern foothills. Its auditory ossicles are peculiar, 

 the stapes having an enormous bullate foot-plate. The ossicles 

 of the other species of Thomomys have not been examined. Of 

 Cratogeomys we have only one species, C. castanops of Baird, 

 originally based on material from near Las Animas. It is found 

 in the region south of the Arkansas River, and near Lamar. 

 Warren notes that it is darker, larger (length 10>^ inches), and 

 heavier built that the Yellow Pocket Gopher, Geomys lutescens 

 of Merriam. This latter animal is widely distributed in eastern 



*For a full account, see Bailey, North American Fauna, No. 39 (1915). See also 

 Pocket Gophers, by W. L. Burnett, Circular 10, Office of State Entomologist (1914). 



