VARIATIONS OF RODENTS 



235 



(161566BS) they examined from the Kaibab Plateau, I have assigned 

 those from the North Rim to grammurus. 



Size: From an examination of the available body and skull measure- 

 ments, it seems that the subspecies utah and grammurus are too nearly 

 alike in size to be separated on this basis. Those from the North Rim 

 (Table 3) are large and equal or exceed the average measurements for 

 both Utah and grammurus from adjacent areas. There appears to be a 

 cline of decreasing relative length of tail from southeastern Colorado 

 (where the tail is 82 per cent of head-body length) to Nevada (where 

 the tail is 73 per cent for males and 71 per cent for females). In this 

 character, the rock squirrels from the North Rim (74 and 71 per cent 

 for males and females, respectively) agree with those from Nevada. 



Sexual dimorphism: ]\Iales usually have slightly larger skulls, longer 

 hind feet and greater head-body length than females, but weigh less. Hall 

 (1946, p. 310) found females to be 97.5 per cent as long as males, but 

 107 per cent as heavy. IV'ly corresponding figures for the specimens from 

 Muav Saddle are 94.5 and 105. 



Both females from the North Rim were suckling young but neither 

 showed evidence of a second pregnancy for the season. 



More collecting needs to be done to determine the kinds and ranges 

 of these rock squirrels. For example, Durrant (1952, p. 482) wrote, 

 "Citellus [ = Spermophilus] variegatus Utah ... is known also from 

 Idaho . . ." but I find no record of its occurrence in that state. Also he 

 {op. cit., p. 119) gave the northern limit of the range of S. v. grammurus 

 along the Nevada-Utah boundary as 37>^° N, whereas Hall (1946, p. 

 311) gave it as 40° N. 



Spermophilus lateralis lateralis (Say) 



Habitat: Golden mantled ground squirrels were common at many 

 stations on the North Rim, particularly in meadows and in forested areas 

 near open water. They did not go as far into the dry forest as did the 

 chipmunks nor were they obser^-ed or taken on the very rim of the 

 Canyon. They were most abundant at Swamp Lake, where six adults 

 were taken. One of these was caught in a gopher trap set in a tunnel 

 of the mountain pocket gopher. The subspecies S. I. lateralis, to which 

 Howell (1938, p. 192) assigned this isolated population on the Kaibab 

 Plateau, occurs widely in Colorado, and its range extends westward 

 along the Uinta Mountains in Utah and thence southward along the 

 High Central Plateau to southwest Utah. 



