Taylor — A New Mountain Beaver from California. 23 



width of cranium, 53.7; alveolar length of superior cheek teeth, 18.7; 

 distance between infraorbital foramina, 16.1; mandible, transversely 

 across angular process, 22.1; greatest length of mandible, 48.4. 



Remarks. — Germane to this discussion are the following facts: For 

 some time it has been recognized that the Aplodontia of the Humboldt 

 Bay district is distinct from its coast-dwelling neighbors. Concerning 

 the degree of its relationship to Aplodontia chryseola of the neighboring 

 montane district interiorly there have been no adequate data at hand. 

 A fairly sharp faunal line separates the Trinity Mountain district from 

 that of the northern liumid coast. At least seven genera of rodents are 

 represented in the two regions by distinct species or subspecies. Conse- 

 quently it is not surprising to find that adequate material shows that the 

 Aplodontia of the coast region is distinct from that in the neighboring 

 montane district. 



It is, however, somewhat surprising to find that the closest affinities of 

 Aplodontia humboldtiana are with A. chryseola rather than with its 

 neighbors on the coast, for the affinities in most groups of mammals 

 would appear to be north and south in the coast districts rather than east 

 and west from the coast districts to neighboring montane districts. At 

 least this seems to be true in the genus Aplodontia, which has the rather 

 compact group of coast-dwelling forms represented by Aplodontia phsea, 

 A. nigra, and A. pacifica, apparently more closely related to each other 

 than to any other members of the genus. Grinnell has shown (An 

 Analysis of the Vertebrate Fauna of the Trinity Region of Northern Cali- 

 fornia, Univ. Calif. Publ. Zool., vol. 12, 1916, pp. 401, 407) that there are 

 few Boreal species, either of birds or mammals, in the Trinity region 

 which are identical with, or show closest affinities to, representatives in 

 the northern humid coast belt. It is of interest that no rodent appears 

 among the species listed by him as illustrative of close affinities in this 

 direction. 



Consequent upon these considerations it appears that Aplodontia hum- 

 boldtiana furnishes an exception to the usual systematic alignment in the 

 region in question, having its closest affinities rather with its montane 

 neighbor to the eastward, than with its lowland neighbors either north 

 or south along the coast. 



