618 U. Ss. P. R, R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
LAGOMYS, Cuv. 
Lagomys, ‘‘ Cuvier, Tableau élémen. 2797.’’ 
No visible tail; ears short and rounded ; hind legs short. Molars — 
The species of this genus are small, the largest not exceeding a Guinea pig in size. They 
are confined to the northern hemisphere, and generally occur in elevated districts. But one 
species is found in North America; this, within the limits of the United States, occurs in the 
region of the Rocky mountains, near the British line, north of which it is more abundant. 
Others occur in Siberia, as well as in central Asia. 
In general appearance the pikas, as they are called in Siberia, bear a not inconsiderable 
external resemblance, both in shape and color, to the wild Guinea pigs (Caviae) of South Ame- 
rica, some of which, too, have the same habit of being among almost Alpine altitudes. This 
is especially the case with the Cavia australis, which in the high regions of Uspallata is found 
in great numbers, and is known as the mountain rabbit. 
‘The pikas present other important differences from the hares besides those above referred 
to. Thus the skull is more depressed and more dilated behind ; the interorbital space more 
contracted ; the supra-orbital process is wanting ; the orbits are directed more upwards; the 
malar bone is prolonged behind greatly beyond the zygomatic process of the temporal, reaching, 
in fact, nearly to the opening of the ear chamber. Instead of the numerous perforations of the 
nasal process of the superior maxillary bone of the hares, there is but one chief opening in the 
same bone in Lagomys. Viewing the skull from below, the bodies of the sphenoids and the 
vomer are brought nearer to the plane of the palate than in the genus Lepus. The posterior 
sphenoid wants the mesial perforations, and the openings on either side of this bone are smaller ; 
the vomer joins the anterior sphenoid, while in the hares an oblong opening separates the bodies 
of these two bones. The incisive openings are sometimes separated from the middle or chief 
palatine openings, but in some species the openings are confluent, as in the hares. The occiput 
is broader than high, and the zygomatic arch remarkably short. 
‘‘In the lower jaw the chief differences consist in the smaller antero-posterior diameter of 
the angular portion, and in the condyloid portion being sloped less backwards; the long thin 
plate representing the coronoid process in the true hares is in the pikas replaced by a small 
tubercle, and there is a second still smaller tubercle placed just below the one just mentioned, 
and, in fact, but little removed from the posterior molar teeth. The mental foramen, instead 
of being placed in the fore part of the jaw, is situated near the middle of the outer surface of 
the horizontal ramus. 
“‘The principal incisor teeth in the upper jaw are broad, but have a very small antero- 
posterior diameter ; each of these teeth has a deep vertical groove on the outer side, and termi- 
nates in two points, there being a strong notch at the extremity. The lower incisors are simple, 
and smaller than the upper. The upper molars are much as in the hares; they have the same 
three transverse ridges of enamel, but on the hinder part of the last molar an extra loop is 
visible, which is placed nearer to the inner than to the outer angle of the tooth; this molar 
corresponds to the penultimate molar of the hare. The lower molars have the grooves in the 
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