234 University of California Publicatians in Zoology [^o^. 21 



well, as its range is separated from that of pacificns by the Klamath 

 River gap. Although intergradation between these two races has not 

 been demonstrated, they are so similar in many ways, and alleni is 

 subject to such geographical variation within its range, that it seems 

 better, for the present, to consider one the subspecies of the other. 

 The segregated Boreal areas in which alleni is found, comprise (a) 

 the small cap of South Yolla Bolly Mountain in Tehama County, 

 apparently separated by twenty miles or so of Transition Zone from 

 (&) the Siskiyou Mountains and Mount Shasta, between which there 

 is uninterrupted distribution, to some extent at least, through the 

 Sisson region. This area is separated from (c) Mount Lassen by the 

 Pit River gap, which in turn, is divided from (d) the main Sierran 

 mass to the south by the Feather River gap, but the latter may or may 

 not be a barrier to the genus (see Merriam, 1899, pp. 69-70). 



In certain respects, the skulls of examples from Mount Shasta 

 show a tendency to approach pacific us (as in rostrum and nasals), 

 but all that I have seen are distinct from the latter. It is unfortunate 

 that the specimen from Little Shasta, which Preble (1899, p. 31) pro- 

 nounced "not typical" pacificus, is not available, but the animal was 

 immature, and I strongly suspect that it may present an appearance 

 similar to a very pale juvenile which I took at Sisson. Average meas- 

 urements, in the flesh, of 10 apparently adult specimens from Mount 

 Shasta: length, 230.5 mm.; tail, 139.8; foot, 33.1. 



Skulls from the Siskiyou Mountains in Trinity County are large, 

 with incisive foramina even larger than in typical alleni, and rostrum 

 varyingly intermediate between that form and pacificus. Average 

 measurements, in the flesh, of twenty apparently adult specimens from 

 Trinity County: length, 231.8 mm.; tail, 140.7; foot, 32.4. 



Skulls from South Yolla Bolly Mountain, in Tehama County, show 

 a very slight leaning towards orarins (small size, small rostrum, and 

 short incisive foramina), as might be expected on geographical 

 grounds, bvit they are definitely distinct from that species and clearly 

 belong to the pacificus-alleni group. The rostrum is slightly shorter 

 than is typical, brain-case proportionally more inflated, incisive fora- 

 mina shorter, pterygoid fossae smaller, and bases of the anteorbital 

 foramina considerably heavier. The dorsal area is slightly paler than 

 usual and there is a yellowish tinge to the underparts of the specimens 

 at hand, which darkens to brownisli mid-ventrally in three skins. 

 However, all of these were taken at the same time, and it is safer to 

 infer, at least until more material is at hand, that the unusual tinge 



