lvon] the hares and their allies 3/1 



ochotonid.e 

 (Plate XCVI, 2) 



The material for making generalizations concerning the sterna of 

 the Ochotonidae is far from being satisfactory. Out of four skeletons 

 but one is fully adult and there is a certain amount of variation 

 among them. It may be that more material would show that there 

 are two or three different types of sterna among the Ochotonidae. 

 Aside from a few minor details the sternum of the only adult 

 Ochotona at hand, No. 91,188, is almost exactly like the sternum 

 of Rouierolagus just described, so that the genus Ronierolagus 

 can be briefly described as a rabbit with the sternum of a pika. The 

 expanded portion of the manubrium is less developed in Ochotona 

 than in Ronierolagus, and rather triangular in outline instead of 

 pentagonal. In other respects the two sterna are similar. The 

 Ocliotona presternum is nearly as long as the mesosternum and 

 slightly longer than the xiphisternum. 



The mesosternum of Ocliotona is in general very similar to that 

 of Ronierolagus. The first and second segments are subequal in 

 length, the second being broader however. The third segment is 

 the longest and broadest of the mesosternum. The fourth segment 

 is the shortest and nearly as broad as the third. Both the third and 

 fourth mesosternal segments are completely ankylosed as they are in 

 Ronierolagus and Limnolagiis. 



The xiphisternum is considerably expanded at the proximal end, 

 but the distal extremity is not much enlarged. It is decidedly shorter 

 than the presternum. 



The seventh rib is attached along with the sixth rib to the sternum 

 at the point of union of the mesosternum with the xiphisternum. 



No. 30,990 Ochotona sa.vafilis, Idaho, is very similar to the above; 

 it is young, however, and the third and fourth pieces of the mesoster- 

 num are not yet fused. 



No. 49,620, from Oregon, has the entire mesosternum narrow 

 and its last two segments separate. 



No. 49,500 Ochotona ladacensis, Ladak, central Asia, has the 

 enlarged portion of the presternum less expanded ; the mesosternum 

 is relatively longer and decidedly narrower than is the mesosternum 

 of 0. saxatilis, the third and fourth mesosternal segments are not 

 fused. The mesosternum as a whole bears considerable resemblance 

 to some of the mesosterna of Sylvilagus. The xiphisternum is rather 

 short. 



