RODENTIA—ARVICOLINAE——AR VI CO LA MONTANA. 
529 
loose and not compact, quite bristly and coarse, with little lustre. The hairs on the back 
measure about half an inch ; those beneath, half as much. The ears are short, and probably 
concealed in the fur in fresh specimens ; they measure but little over half the length of the hind 
foot, (about .4 of an inch,) but about equal the fore foot from wrist; they are sparsely covered 
with rather long hair on both surfaces, except around the meatus. There is a segmental anti¬ 
tragus of moderate size. 
The hind feet are rather short, (.8 of an inch,) about twice as long as the fore foot. The 
toes are rather short, about one-third the whole foot. The thumb is armed with a small blunt 
claw. 
The tail is moderately long, rather more than two-fifths the head and body in the dried skin; 
it is closely covered with appressed stiff hairs of equal length, and terminates in a scanty pencil. 
The prevailing color above is a dull yellowish brown, pretty uniformly mixed with black, and 
rather lighter on the sides. There is nowhere any rusty tinge. Beneath, the color is a dull 
whitish ash, mixed with the plumbeous of the base of the fur. The feet are brownish white. 
The tail is brown above; dirty white beneath, with a moderately distinct line of demarcation. 
The skull of this species is broad and short, 1.12 X 62, or as 100 : 56. The distance from 
the molars to the base of the incisors is about one-third the distance from incisors to occiput, 
(.35.) . The line of molars measures .24. The posterior upper molar has three external salient 
angles in addition to the rounded crescentic lobe, which is simple, or without a supplementary 
lobe on the inner side, springing from the concavity. The anterior lower molar has one posterior 
closed triangle, three interior, and two exterior, with a trefoil lobe anteriorly, the lateral divisions 
of which each add a salient angle, making five interior and four exterior. The anterior and 
middle molars are nearly of equal width. 
This species is most nearly allied to Arvicola edax, resembling it in size and color. The feet 
and ears, however, are much smaller, as will be seen by the table of measurements. From A. 
townsendii its grayer colors, smaller size, smaller ears and feet, &c., will at once distinguish it. 
It is with very considerable hesitation that I refer No. 370, from Monterey, to this species. 
It comes very near A. edax in color, but agrees much more closely with the present in the short 
feet and ears. The line of separation between the upper and under colors of the tail is much 
more strongly defined. The feet are dirty white. The principal ground for suspicion as to the 
identity of the two species is based on the striking dissimilarity in the skulls. The proportions 
of breadth to length in V7V are 1-03' to .61, or 100 : 60 nearly, quite an unusual proportion 
in this group. The distance from upper molars to base of incisors (.30) is not quite one-third 
that from incisors to occiput; the crowns of the upper molars measure .25, or about one-fourth 
the total length of the skull. The anterior lower molar differs widely in having an additional 
lobe to the anterior trefoil on the inner side. There is one posterior closed triangle, three inte¬ 
rior, and two exterior, as usual; the anterior lobe, however, is not a simple trefoil open loop, 
as in the other species, but its anterior branch, instead of rounding off antero-internally, has 
a salient angle there, giving rise to six of such angles on the inside of this tooth and five on the 
outside, the anterior of the latter rounded, however, leaving but four very sharp angles. 
As, however, the teeth and skull often vary considerably in the same species, I do not feel at 
liberty to regard this specimen as distinct without further materials, although its locality is 
widely remote from that of the rest. Should future examinations substantiate the species, I 
would propose for it the name of A. trowbridgii , from its accomplished discoverer and collector, 
Lieutenant Trowbridge. 
67 L 
