208 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
that they might be described in identical terms. The ears are the notable 
feature; and they have been so carefully and minutely described by Baird, 
from the same specimens now lying before us, that, as in case of our diagnosis 
of Chilotus, we may best repeat his words :— 
“The ears are low, orbicular, the membrane thickened, the margins or 
conchal portions much inflected or incurved, like a half open apple-blossom, 
the concha being inflected all around. The antitragus is well developed, but 
rather low. The surfaces of the ear appear perfectly naked, with, however, 
a ciliation of long hairs towards the roots of the concha, on the dorsal surface. 
A close examination of the auricle in the dried specimen shows a few scat- 
tered very short white hairs. The structure of the ear, though in many 
respects similar to that of A. pinetorum, is yet essentially different. Thus 
the upper and lower roots of the margin of the ear meet anteriorly so as to 
form even a low rim to the meatus anteriorly completely enclosing the aper- 
ture; the edge of the conch is inflected; the region inside the auricle, around 
the meatus, naked, and the antitragus so much developed as to be capable of 
completely closing the meatus. In A. pinetorum the roots of the upper and 
lower margins of the ear are widely separated, by a space of a quarter of an 
inch, the space between these roots and anterior to the meatus being perfectly 
plane; the edges of the concha or auricle not inflected at all; the inner space 
around the meatus partly hairy; the antitragus very slightly developed, not 
valvular nor capable of closing the meatus at all.” 
The skull of this species (7333) is rather broad for its length (0.92 0.51), 
but has nothing diagnostic about it except the dentition, which curiously 
unites that of Myonomes with that of Pedomys or Pitymys. ‘hus, the 
middle line of enamel on the front lower molar extends so far forward as 
to separate the anterior on angles each side, and cut these off from the dentine 
island of the anterior trefoil, so that an additional closed triangle is produced 
on each side. The middle upper molar develops no snag on its postero- 
external triangle; and the last upper molar has but one external angle and a 
long narrow posterior Y. ; 
A miserable specimen from Oregon (No. 3734, U. S. Expl. Exped.) is 
labeled “oregona”, but is not this species at all, being a Myonomes. The 
measurements of the three specimens below given will show to some extent 
the variations in size and shape. At present, the species is only reported from 
the Pacific coast of the United States. 
