406 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
extension seen in the latter. The posterior palatine foramina form a large 
circular opening, which is not extended forward beyond the intermaxillo- 
maxillary suture. The palate, owing to the more depressed form of the skull, 
is much nearer the vomer than in Lepus. The angular process of the lower 
jaw is narrower, longer, and more recurved than in the Hares. The condylar 
process is broad and quadrate, and the condyles have a very great antero- 
posterior development, relatively four times greater than in Lepus; the 
coronoid process is placed lower, and forms a mere tubercle, with a second 
smaller tubercle near the last molar. The foramen mentum is remarkable 
for its posterior position, being about opposite the middle true molar, instead 
of considerably in advance of the first premolar, as is usually the case. | 
The small posterior upper molar seen in Lepus is wanting; the remaining 
upper molars do not differ materially from those of Lepus, except that they 
are much more deeply grooved on the inner side. The lower molars, how- 
ever, are very different from those of Lepus, they being so deeply divided by 
the lateral grooves that the triturating surface presents a series of acute 
triangles with open intervals, somewhat as in Arvicola. The cutting-edge of 
the front upper incisor is gouge-shaped instead of chisel-shaped, as in Lepus 
and most other Rodents, the cutting-edge being hollowed on the inner side. 
The anterior face is divided by a deep longitudinal groove into two unequal 
moieties, the outer of which is nearly three times as wide as the inner, and 
considerably longer, generally exceeding the inner, in Lagomys princeps, by 
about 0.05 of an inch. The cutting-edge is consequently deeply notched ; the 
bottom of the notch, formed by the groove, being sometimes 0.12-of an inch 
below the outer edge. The lower incisors are rounded anteriorly, and lack 
the groove seen in the upper incisors. 
The Pikas are nearly tailless, and the general furm of the body and limbs 
is much as in the Arvicole. They hence lack the greatly disproportionate. 
development of the hind limbs seen in the Hares. The clavicles are also well 
developed. The toes are five in front and four behind, armed with short, 
arched, compressed nails, and at the base of each toe is a prominent, naked 
pad. The pelage is much firmer than in the Hares, with less of the soft, 
downy under-fur, and more resembles the pelage of Arvicola. They are weak, 
sedentary animals, living among loose rocks in alpine localities, generally on 
or near the summits of high mountains, and are apparently. strictly diurnal in 
their habits. They are social in their dispositions, living generally in com- 
