618 TJ. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



LAGOMYS, Cuv. 



Laffomys, "CuviER, Tableau Kidmen. 1797." 

 No visible tail ; ears short and rounded ; hind legs short. Molars 5^5 . 



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 Kocky mountains, near the British line, north of which it is more ahundant. 

 Others occur in Siheria, as well as in central Asia. 



In general appearance the pikas, as they are called in Siberia, hear 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 



