498 University of California Publications in Zoology [Vol. 16 



senee of distinct postorbital processes on the jugal; smaller than 

 Aplodontia calif or nica Columbiana and Aplodontia calif omica rainieri. 

 Comparisons. — In examples of Aplodontia rufa grisea the brown 

 coloration ranges from light ochraceous-buff to light buff, while in 

 A. r. rufa the range in coloration is from near tawny to light ochra- 

 ceous-buff; grisea for the most part lacks the distinct brown wash so 

 often present in rufa. Cranially, grisea tends to have interpterygoid 

 fossa narrower than in rufa, audital tube of smaller caliber, post- 

 orbital process indicated on the jugal in some specimens, and lesser 

 mastoid width. 



Aplodontia rufa grisea may be separated from A. r. olyrnpica, in 

 the usual instance, only by the different development of postorbital 

 process on the jugal. In grisea these processes are weakly indicated 

 in a few examples, in olyrnpica they reach their maximum of develop- 

 ment in the genus. Even this character cannot always be relied upon 

 as certainly separative, since the postorbital processes are sometimes 

 weakly developed in olyrnpica. Available skins of grisea and olyrnpica 

 are not strictly comparable, for the majority of the specimens of 

 grisea were collected in winter, and the series of olyrnpica was taken 

 in summer. Seasonal variation in the genus is usually exceeded by 

 individual variation, however, so cross-comparisons may perhaps legit- 

 imately be made. A summer skin of grisea from Sumas, British 

 Columbia (no. 88008, Biol. Surv. Coll.), is identical in coloration with 

 certain summer specimens of olyrnpica. Comparison of this skin with 

 the entire series of examples of olyrnpica, however, demonstrates the 

 presence of more blackish dorsally in the latter and more of a tendency 

 toward a brown wash ventrally. 



Aplodontia rufa grisea is smaller than Aplodontia calif omica 

 columbiana in both external and cranial characters, with slighter tend- 

 ency to whitish ventrally; tendency for zygomatic and mastoid widths 

 to be more nearly equal, lesser tendency to accentuation and approxi- 

 mation of temporal ridges, and incisive foramina tending to be shorter. 

 From A. c. rainieri, grisea is separated by smaller size and by having 

 basilar length averaging less, maximum length of nasals in grisea 

 about equal to minimum in rainieri, nasals tending to be narrower 

 anteriorly and posteriorly, interpterygoid fossa averaging narrower, 

 mastoid width of cranium averaging less, conformation of rostrum 

 more plane. 



Material. — Fourteen specimens, as follows: one (no. 88008, Biol. 

 Surv. Coll., taken by A. C. Brooks) from Sumas, British Columbia; 



