432 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



The incisive foramina are variously shaped ; they may have an 

 ■elongated, triangular form, as in Ochotona roylii, but more usu- 

 ally they are divided into two portions — a smaller anterior one 

 just behind the upper incisors, and a larger, rather pyriform one, just 

 anterior to the bony palate — by the uniting to a greater or less pxi-ent 

 of the posterior ventral portions of the two premaxillary bones. 



The zygoma is moderately heavy ; at its antero-inferior angle is a 

 well-marked tubercle ; its posterior free extremity is very long. 



The maxilla of Ochotona is not fenestrated as it is in the Leporidse. 

 Instead there is a single large, roughly triangular opening in the 

 -upper part of the nasal portion of the maxilla. In Ochotona roylii, 

 however, the triangular opening is more elongated than in the other 

 .species, and just inferior to it there is a very slight amount of 

 fenestration. 



The mandible of Ochotona has a very wide ascending ramus and 

 long condyle ; the notch between the ascending ramus and the angular 

 process is large. No groove or thin plate of bone is found on the 

 anterior surface of the ascending ramus of the mandible, as in the 

 Leporidse, but a prominent tubercle occurs there which is lacking in 

 the latter family. The mental foramen is situated on the side of the 

 horizontal ramus, directly under the last lower molar. 



Teeth (pi. xci, 2; fig. 44, 25.) — The first upper incisors of Ocho- 

 tona have each a single, simple groove. Their cutting edge is very 

 sharp ; that portion external to the groove is much produced down- 

 ward, the internal portion only moderately so produced. In this 

 manner an unequally sided V-like notch is seen on the front cutting 

 edge of each tooth, with the groove at the point of the V. 



The second upper incisors are small slender teeth placed directly 

 behind the first. The lower incisors, a single pair, are longer, 

 .slenderer, and more pointed than the corresponding teeth in Lcpns 

 and its allies. 



The first upper premolar is small, with a single reentrant angle on 

 the inner half of the anterior face. 



The second upper premolar has a reentrant angle on its anterior 

 .face, extending to the middle of the tooth and thence toward the 

 outer edge. There is also a broad, shallow angle on the internal face 

 of this tooth. 



The three remaining upper jaw teeth possess each a single reentrant 

 angle on the internal face, extending all the distance across the 

 tooth, very much like the reentrant angles of the Leporidse, but 

 without any crenation. The last tooth has a projecting loop of 

 enamel, from its posterior aspect, thus differing from the two teeth 

 immediately in front of it. 



