500 University of California Publications in Zoology [Vol.16 



broader, zygomatic arches heavier and more expanded at posterior 

 root, caliber of audital tubes tending to be less, a more pronounced 

 tendency apparent toward approximation of temporal ridges, less of 

 a hollow in skull outline dorsally (looking at skull in side view). 



Comparisons.— In coloration dorsally Aplodontia calif or nica Colum- 

 biana is not conspicuously or appreciably different from A. c. rainit ri. 

 The tendency observable in males of columbiana to have irregular 

 patches of white hair beneath is not expressed in available examples 

 of rainieri. Total length externally is nearly 14 per cent greater in 

 columbiana, figured on the basis of the total length in the type of 

 rainieri and that in nine specimens of columbiana. The following 

 cranial measurements average greater in columbiana than in rainieri: 

 length and width of nasals, length of incisive foramina, zygomatic 

 width, mastoid width, and greatest length of mandible. Available 

 material shows the length of nasals in columbiana to be absolutely 

 greater than in rainieri. 



From Aplodontia calif or nica calif or nica the British Columbian 

 form is distinguished, among other characters, by its larger general 

 size, and by having, in the usual instance, zygomatic arches less square 

 anteriorly, lighter in weight and more expanded in the region of the 

 posterior root, caliber of audital tubes less, and external auditory 

 meatus of different shape. 



Comparison with Aplodontia rufa grisea is perhaps not strictly 

 necessary. From this race A. caU for nica columbiana is separated by 

 the more pronounced tendency observable in columbiana to have irreg- 

 ular white patches beneath, by larger size in general, different outline 

 of nasals, heavier zygomatic arches and their greater expansion pos- 

 teriorly, lesser caliber of audital tubes, and different outline of ex- 

 ternal auditory meatus. The last-mentioned character is a conspic- 

 uous one, the meatus in columbiana being pinched up anteroposteri- 

 orly. making the dorsoventral diameter of the meatus greater than 

 the anteroposterior. In grisea the outline of the meatus approximates 

 a circle. 



Material. — Nine specimens, all from British Columbia: four (nos. 

 1892-1895, Mus. Comp. Zool., taken by W. C. Colt) from Lake House, 

 Hope; five (nos. 1896-1900. Mus. Comp. Zool., taken by W. C. Colt I 

 from Roab's Ranch, Hope. 



Measurements. — Of type ' adult male): total length, 470 mm.; 

 tail, 22; hind foot, 20; width of nasals, 13.0; length of incisive fora- 

 men, 7.8; zygomatic width, 66.0: mastoid width, 61.2; alveolar length 



