lvon] the hares and their allies 373 



the last rib to bear a spine-like tubercle on the rio-ht side is the 

 seventh, while on the left side it is the sixth. The shafts of the 

 anterior ribs are not widened ventrally. 



The spines of the tubercles are very small in Pronolagns, and are 

 last found in the seventh pair of ribs. The shafts of the ribs are 

 relatively narrow and there is no indication of the wide expansion 

 found in Lepiis. Decidedly the widest part of the rib is just behind 

 the spine. 



Roincrolagus very closely resembles Pronolagiis in regard to the 

 ribs, Ijut the spines of the tubercles are last found on the sixth pair. 



OCHOTONID.^I 



(Plate XCIV, 9) 

 In the Ochotonid?e there are seventeen pairs of ribs of which the 

 first seven are attached to the sternum by means of costal cartilages, 

 the last seven pairs or about that number have no ventral attach- 

 ments, while the three intermediate pairs are attached to the costal 

 cartilages of the ribs in front. The ribs are all slender and weak 

 compared with the ribs of the Leporid?e and none of them possesses 

 spine-like, non-articular portions of tubercles, but just behind the 

 tubercles the more anterior ribs are quite broad and heavy. 



CLAVICLE 



Leporidj. 

 (Plates XCV, 2, 5; XCVI, i) 

 In the LeporidcC the clavicle is probably always present as a small 

 curved, slender bone, about fifteen millimeters long. In most of 

 the skeletons, however, the clavicles are wanting, undoubtedly the 

 result of faulty preparation. In only four of the skeletons at 

 hand have these bones been found. The uncleaned skeletons show 

 that the clavicle does not articulate with either the sternum or 

 the scapula as it does in those animals where it is well developed. 

 Ligamentary tissue extends from its inner end to the presternum, 

 while the outer end is attached to a piece of cartilage placed on the 

 summit of the greater tuberosity of the humerus. In his account of 

 the genus Roincrolagus (Proc. Biol. Soc. Washington, x, 1896, 

 December 29, p. 171) Dr. ]\lerriam says: "The clavicle is complete 

 and articulates directly with the sternum (fig. t,t,) — a thing that 

 never happens in the genus Lcpus.'' Whether that is the case with 

 any of the other genera of the LeporidcC can not be told, owing to 

 the faultv methods of cleaning the skeletons. It might be thoug^ht 



