98 
JOUENAL OF MAMMALOGY 
DESCRIPTION OF A NEW SPECIES OF PHENACOMYS FROM 
OREGON 
By a. Bkaziek Howell 
[Plate 7] 
Among some skins with uncleaned skulls, which were kindly loaned 
me for study by Stanley G. Jewett, was a Phenacomys which appeared 
to belong to a new species; and after the skull was cleaned all doubts 
of this were removed. Mr. Jewett has generously given me permis- 
sion to describe this new form, which may be known as 
Phenacomys silvicolus new species 
FOREST LEMING-MOUSE 
Type. — Young adult female; No. 1214, Coll, of S. G. Jewett; 5 miles southeast 
of Tillamook, Tillamook County, Oregon; October 25, 1916; collected by Peter 
P. Walker; Orig. No. 40, Coll, of Alex. Walker. 
Diagnosis. — Externally, closest to Phenacomys longicaudus, with a general 
appearance and tail very similar to that form; but darker and with smaller ears. 
The skull is longer than that of longicaudus of corresponding age, with narrower 
braincase having temporal ridges, with much heavier molariform teeth of a 
different pattern, and with pterygoid plates which flare anteriorly on their outer 
edges. 
Description. — The hairs on the back of silvicolus are fine and long, some of 
them reaching a length of 15 mm. The bases are plumbeous, and the distal 
ends sayal brown, sparsely tipped with black. The coloration is slightly paler 
on the sides, and rather abruptly white on the ventral surface, the hairs of the 
latter area having plumbeous bases. The feet are soiled whitish with long toes 
and claws as in longicaudus; and the tail is covered with long, blackish hairs as 
in that species. The ears are small and do not project beyong the body hairs. 
The skull is quite different from those of P. orophilus, P. albipes, or P. longi- 
caudus. In comparison with the last-named species, which is evidently its clos- 
est relative, the skull of silvicolus exhibits the following characters. The brain- 
case is flattish, long and comparatively narrow. The nasals are somewhat 
constricted at a point posterior to the middle, with the ascending extremities of 
the premaxillae narrower. The zygomatic processes of the maxillae slope rather 
evenly from the rostrum, and the zygomatic width is greatest in the anterior 
region of the jugals, with the latter converging somewhat posteriorly. The 
temporal ridges are very pronounced and are parallel in their posterior halves, 
thence joining the vertical ridges of the squamosals. The postorbital processes 
of the squamosals are poorly developed and are not ‘‘peg-like.” The incisive 
foramina are large and are not in the least constricted posteriorly. There is a 
distinct “hump” at the juncture of the basi-occipital with the basi-sphenoid. 
