184 The American Naturalist. [February 
_dylar ramus short and heavy with strong posterior shoulder forming a 
knob at base of condyle, containing the greatly extended root of lower 
incisor. Coronoid process, stout, erect and triangular. Angle very 
short and massive. at Pa 
Body probably stouter than in Arvicola. Tail over half the length 
of head and body, sparsely and evenly coated with short spines and ter- 
minated by a well-defined pencil of slender hairs. Feet five-toed, each 
with five tubercles; claws long and slender. Whiskers pronounced, 
the longest reaching behind ears. 
Aulacomys has {the superficial appearance of Arvicola but with a 
very long and apparently naked tail and heavy whiskers. Cranially, 
it combines the molar dentition of Arvicola with the incisor dentition 
of Synaptomys. ` In these very respects, however, it differs from both 
genera—from Arvicola in the five-angled formation of the anterior sec- 
tion of the first lower molar, and from Synaptomys in the length, nar- 
rowness, protrusion and central sulcation of the upper incisors, also 
in the extension of the roots of the lower incisors far beyond the last 
molar. 
The dentition of Aulacomys shows, in the number of angles of the 
anterior lower molar, an approach to the extinct form, Arvicola (Anap- 
togonia) hiatidens Cope, from the bone caves of Pennsylvania’ but dif- 
fers radically from it in the isolation of the triangles. 
The absence of supra-orbital ridges, the posterior prolongation of the 
nasal premaxillary processes beyond nasals, the acute post- 
notch, the shape of the pterygoid fossa and the massiveness of the 
posterior members of mandible are all, in a greater or less degree, di- 
agnostic of Aulacomys as distinguished from other Arvicoline genera. 
Specific characters.—Type, No. 1358; Ad., 2. Col. of S. N. Rhoads, 
Lake Kichelos, Kittitas Co., Washington [Alt. 8,000 ft.], September, 
1893. (Col. by Allan Rupert.) : 
Description—Characters as decribed for genus. Above, reddish- 
brown, lined with black. Pelage, basally, everywhere plumbeous. 
Below, hoary plumbeous, lightest on throat. Upper parts of feet black- 
ish. Tail very slightly darker above, than below. Ears not promi- 
nent, well-haired on both sides and with distinct valvular antitragu 
Whiskers black. $ 
Measurements (taken in flesh by collector).—Total length 17 
tail 70 ; (taken from damp, relaxed skin), hind foot 27; ear 10; pe? 
7. 
1Proc, Soc. Amer. Philos. 1871, P. 92: 
?Millimeters. 
