41 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 45 



and fourth segments are completely ankylosed so that the whole meso- 

 sternum is composed of but three separate pieces instead of the 

 usual four. The xiphisternum is long and slender and about equally 

 •expanded at each end. 



In all the other genera except Romerolagus, the sixth and seventh 

 pairs of ribs are attached to the last piece of the mesosternum. In 

 these two genera the last rib attached directly to the sternum is 

 the sixth, the seventh rib being attached to the cartilage of the sixth 

 near the point where the latter joins the mesosternum. 



The spine-like portions of the tubercles of the ribs in Liinnolagns 

 are well developed, but are not conspicuous, owing to the fact that 

 the angle between the tubercle and the posterior edge of the rib is 

 iilled in with bone, making that part of the rib very wide, so that it 

 is distinctly the widest portion of the rib. In the single skeleton at 

 hand the last rib to bear a spine-like tubercle on the right side is the 

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

 anterior ribs are not widened ventrally. 



Shoulder Girdle and Upper Extremity. — The scapula (pi. xcvii, 6) 

 of Liiimolagiis is different in form from the same bone in Lepiis and 

 in Romerolagus but shows nothing tangible by which it can be dis- 

 tinguished from the scapulae of the other genera. It is relatively 

 narrow, the superior border relatively convex, the antero-superior 

 angle moderately pronounced, and the supraspinous fossa relatively 

 narrow. 



There is little about the humerus of Liiuuolagus by which it can be 

 distinguished from the humeri of many of the other genera, but 

 the groove subtending the internal condyle is rather less marked than 

 in any of the Leporidse except Romerolagus. The external condyloid 

 ridge is short but comparatively wide, a trifle more conspicuous than 

 it is in the other genera except Romerolagus. 



The form, relative sizes, and positions of the radius and ulna (pi. 

 xcviii, 5) are quite alike in Limnolagus and in Sylvilagus. These 

 bones are subequal in size ; the ulna is not reduced in the middle of 

 its shaft ; it is situated external to the radius, rather than behind it. 

 Both bones are moderately slender. The radius is equal to the 

 humerus in length. 



The carpus, the metacarpus, and the phalanges of Limnolagus are 

 entirely similar in form and position to these same bones in any of 

 the Leporidse, as mentioned in the general account of the wrist and 

 hand (page 378). 



Pekns and Lou'er Extremity. — Limnolagus has wide ilia, much 

 hke those of Lepus, but the antero-superior angle is not obliquely 



