VARIATIONS OF RODENTS 243 



out of eighteen available from De Motte Park are particularly large 

 (type male, 180 mm and average of four topotype females, 164 mm). 

 My largest specimen, a female, measured 162 mm. As will be pointed 

 out in subsequent accounts, there is a geographic relationship between 

 the boreal mammals of the Kaibab Plateau and those of the High 

 Central Plateau of Utah. I think the relationship is closer than Goldman 

 anticipated, for he wrote (1938, p. 335) of the subspecies in southern 

 Utah, "... paroivanensis is more closely allied to kaibabensis than to 

 any other known form, but the smaller size and cranial features pointed 

 out are separative." Having no comparative material I cannot judge 

 the cranial differences, but the head-body measurements of my specimens 

 (159 mm and 155 mm for males and females, respectively) agree rather 

 closely with Goldman's {op. cit.) lengths of 159 mm and 148 mm for 

 paroivanensis. 



Sexual dimorphism : On the North Rim the animals from resistant 

 soils are not only smaller, but the sexes are nearer the same size, females 

 averaging 97 per cent as large as males whereas in De Motte Park they 

 are 91 per cent as large. 



Color: The most distinctive color character of the northern pocket 

 gopher of the North Rim is the white markings on the ventral side, par- 

 ticularly anteriorly. The chin and openings to the cheek pouches are 

 white. Occasionally one has a white pectoral or a white inguinal spot or 

 a bold, white "V" on the chest. 



The character of white ventral markings was mentioned in the 

 original description (Bailey, 1915, p. Ill; ". . . chin usually, and spot 

 on breast sometimes, white . . .") of T. fossor, the kind to which the 

 North Rim form was originally assigned. In the original description of 

 T. t. kaibabensis (Goldman, op. cit.) mention was made not of the 

 white ventral spots but rather of anterior white fleckings (presumably 

 on the dorsum; see Warren, 1942, p. 164) which the author considered 

 an erratic factor. This flecking does not appear in my specimens from 

 the North Rim. Goldman {op. cit.) noted a close relationship between 

 kaibabensis and fossor but suggested that "a new group alignment should 

 be based on more complete studies than I have made." 



The character, white ventral markings, is characteristic of the sub- 

 species dttrranti (Kelson, 1949, p. 143) in southeastern Utah, but the 

 recognized ranges of both durranti and fossor lie on the opposite side 

 of the Colorado River from that of kaibabensis. It seems probable that 

 the size character of kaibabensis has been over-estimated and that the 

 white ventral markings of the subspecies have been ignored by most 



