41 S SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



terior portion well marked. Owing to an extra fold of the reentrant 

 angle the posterior face of the anterior portion of this tooth has a 

 slight indentation not seen in the other genera. 



Vertebral Column. — The greatest development of the shortened 

 type of cervical vertebras (pi. xcii, lo) is seen in Pronolagus. The 

 costal process stands out very far from the body of the vertebra ; 

 the process itself is narrow, that is, its antero-posterior dimensions 

 are relatively much less than they are in the other genera. The 

 cephalad and caudad projecting spines of the costal processes are 

 apparently not well developed, but they have a somewhat worn or 

 damaged look in the only skeleton. The general appearance of the 

 cervical vertebrae in Pronolagus, seen from below, is much the same 

 as in Ochotona. 



The spines of the anterior thoracic vertebrae are equal to about 

 two and a half times the length of their centra. The eleventh 

 thoracic is the anticlinal vertebrae. Metapophyses are developed in 

 the last four thoracic. 



The transverse process of the lumbar vertebrae (pi. xciii, 3 ) of 

 Pronolagus is of medium length, the longest equaling the length 

 of the centrum to which it is attached. It is not so much enlarged 

 at the free extremity as it is in other genera. It is wide at the 

 base where it comes from the whole side of the centrum, resembling 

 Lininolagus in this respect, but the posterior border of the process 

 is not so strongly concave as in that genus and the process itself is 

 more slender. The spinous processes are low and triangular, like 

 those of Lininolagus, Romerolagus, and Pacilolagus. The hypo- 

 physes are injured in the only available skeleton. Probably the 

 second was the longest. 



■ The sacrum differs in no way from the description given in the 

 general account, page 362. 



All but two of the caudal vertebrae are missing. These two 

 resemble the sacral vertebrae in form. 



Sternum and Ribs (pis. xcvi, 3; xciv, 3). — The posterior two- 

 thirds of the presternum is much compressed, but not keeled; its 

 anterior third is somewhat enlarged, resembling that portion of the 

 presternum of Limnolagus. The first pair of ribs is attached at the 

 junction of the first and second fourths. The mesosternal segments 

 are more compressed laterally than they are in any of the other skele- 

 tons and each succeeding one is a trifle shorter than the one imme- 

 diately in front. The xiphisternum is a little shorter than the prester- 

 num, is comparatively stout and about equally enlarged at each end. 



The spine-like portions of the tubercles of the ribs are very small 



