HOWELL — NEW PHENACOMYS FEOM OREGON 
99 
and the anterior portion of the latter is very narrow, forming considerable vacu- 
ities between it and the pterygoids. The pterygoid plates are unusual in that 
they gradually form lateral shelves anteriorly, and the interpterygoid fossa is 
wide, with the palatal pits more pronounced, although smaller, than in longi- 
caudus. The audital bullae are slightly larger. 
The molariform teeth are even heavier and broader than in oropMlus, with 
the tooth row considerably longer than in longicaudus. The teeth are further 
characterized by the wide, sweeping lines of the enamel folds, and by the tendency 
of all the molar angles in the lower jaw to remain open. This species of Phena- 
comys is unique in having not more than three closed triangles in Ml. There 
are no closed triangles in S©, and the antero-external loop is wide open. MS is 
simple and somewhat as in longicaudus. The upper molariform teeth show no 
notable peculiarities in the enamel pattern. 
Measurements. — Type: Total length, 191^ mm.; tail, Sl^; foot, 32b Length 
of skull, 25.1 ; zygomatic width, 14.4; interorbital width, 3.4; mastoid width, 11.8; 
upper molar row, 5.9. 
Remarks. — The type specimen was found dead on a log on a ridge 
which is covered with first-growth Douglas fir {Pseudotsuga taxifolia). 
The writer spent several weeks in this region during September, 1920, 
and, with the generous cooperation of P. P. Walker and A. Walker, to 
both of whom he is deeply indebted, made a search for this animal. 
All convenient patches of second-growth fir were searched for nests, 
and many hundreds of traps set without result. Virgin timber was 
also examined, but with very httle hope of success, for the trees are so 
large, and so festooned with long moss, that each might contain a 
score of hidden nests. 
P. longicaudus is the only species of the genus that is definitely 
known to lead an arboreal fife. Also, it was previously the only known 
form with a long, hairy tail. Our knowledge of the habits and char- 
acters of other families (e.g., Sciuridse) gives us grounds for presuming 
that hairiness of tail may be considerably increased by a life in the 
trees. The tail of silvicolus is just as hairy as is that of longicaudus, 
and, in addition, both have toes and claws that are unusually long 
and well fitted for climbing. Hence, it is a logical conclusion that one 
species is just as arboreal as the other. 
Mr. Jewett informs me that longicaudus has been taken as far north 
as the Columbia River, so this form probably occurs in scattered 
colonies throughout the coast district of Oregon. The type locality of 
silvicolus is typical of all the humid, timbered area of that state, and 
one may presume that the new species is rather widely distributed. 
1 Collector’s measurements; that of the foot is obviously an error and should 
be 22 mm. 
