LYONJ THE HARES AND THEIR ALLIES 435 



slightly wider, with faint indications of lateral projections ; the rest 

 of the series consists of short, flattened bodies. The single Asiatic 

 skeleton has mainly the same character of the caudals, but the in- 

 dividual vertebrae are relatively wider throughout. 



Stcrnuiii and Ribs (pis. xcvi, 2; xciv, 9). — The material for 

 making generalizations of the sterna of Oclwtona is far from 

 satisfactory. Among 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 in the Ochotonidse. 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 Romerolagus. The expanded position of 

 the manubrium is less developed in Ochotona than in Romerolagus, 

 and rather triangular in outline instead of pentagonal. In other re- 

 spects the two sterna are similar. The presternum is nearly as 

 long as the mesosternum and slightly longer than the xiphisternum. 



The mesosternum of Ochotona is. in general, very similar to that 

 of Romerolagus. The first and second segments are subequal in 

 length, the second, however, being broader. 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 

 Romerolagus and Limnolagns. 



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 meso- and xiphi-sternum. 



No. 30,990 Ochotona saxatilis, from Idaho, is very similar to the 

 above; it is young, however, and the third and fourth pieces of the 

 mesosternum are not yet fused. 



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

 its last two segments separate. 



No. 49,500 Ochotona ladaccnsis, has the enlarged portion of the 

 presternum less expanded, the mesosternum is relatively longer and 

 decidedly narrower than is the mesosternum of O. 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. 



In Ochotona there are seventeen pairs of ribs, of which the first 

 seven are attached to the sternum by means of costal cartilages ; the 



