244 DURHAM 



writers. A reconsideration of the size factor would decrease the assumed 

 gap between kaibabensts and parowanensis, and the size- and pattern-gap 

 between kaibabensis and both durranti and fossor. 



Goldman apparently ruled out white spotting as a genetic factor. Is 

 this character then an environmental one? If we say no, we will have 

 to explain why similar patterns of white spotting occur in both the Botta 

 and the northern pocket gophers on opposite sides of the Grand Canyon. 

 Furthermore, a study of Table 3 reveals an unexpected similarity in size 

 (except for length of tail and ear) between the Botta pocket gophers 

 and the northern pocket gophers of the North Rim. It seems to me that 

 there is some environmental basis for this convergent evolution. 



Peromyscus crinitus stepliensi Mearns 



Habitat: A single specimen of the canyon mouse was taken on a ledge 

 just over the Rim at Point Honan, 7950 ft. elevation. This is apparently 

 a new record for this species on the North Rim. This mouse of the 

 Sonoran Life Zone (Bailey, 1935, p. 18) occurs sparingly at such high 

 elevations (Hall, 1946, p. 504). Bailey (1931, p. 161) made two ques- 

 tionable references to its abundance in the Grand Canyon. The second 

 reference was to Merriam's (1890, p. 62) discussion of Hesperomys 

 [Peromyscus\ eremicus which Bailey apparently confused with P. cri- 

 nitus. Perhaps his first reference also concerns eremicus. 



Size and color: Judging from the single specimen available, the can- 

 yon mouse from the North Rim may be assigned to stephensi, the designa- 

 tion for those in the Grand Canyon north of the Colorado River. The 

 specimen resembles this subspecies in gray color, short head-body length 

 (77 mm), and unusually long tail (121 per cent of head-body length). 

 Osgood (1909, p. 232) and others give the Grand Canyon as an area 

 of intergradation for the canyon mouse. It is therefore not surprising 

 to find that this specimen from the North Rim resembles both the race 

 doutti on the same side of the Colorado River in southeast Utah and 

 auripectus (Durrant, 1952, p. 303) on the opposite side of the River 

 in long hind foot, a faint pectoral spot, heavily-haired tail and large 

 skull, i.e., in length of nasals, zygomatic breadth and breadth of brain 

 case. The hairs of the tail are approximately 2 mm, 4 mm, and 8 mm long 

 at the base, the middle and the distal parts of the tail, respectively. 



Peromyscus maniculatus rufinus (Merriam) 



Habitat: The deer mouse is the common white- footed mouse of the 

 North Rim and occurs in a variety of habitats from barren cliffs along 



