466 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



centra are enlarged. In the lumbar region, especially its hinder part, the 

 centra are very large, indicating powerful and muscular loins ; the neural 

 spines, which increase in length posteriorly, are not much shorter, pro- 

 portionately, than in the existing genus, but much more slender, and have 

 a strong forward inclination ; the metapophyses and anapophyses, on the 

 other hand, are much more prominent, while the transverse processes are 

 quite similar in the two genera. 



The sacrum also is much like that of Dolichotis, but consists of only 

 three vertebrae, the first of which alone is in contact with the ilia; the 

 second and third vertebras have very long and slender, cylindrical centra ; 

 the spines, which are separate, not fused into a continuous ridge, are 

 elongate, though shorter than in the modern genus. The short tail also 

 is very much as in the latter, but is slightly longer and thinner, and the 

 spines of the anterior caudals are not so long. Chevron bones were prob- 

 ably present, though none have been found. 



The ribs, especially in the anterior part of the thorax, are much more 

 slender and rod-like than in Dolichotis. The sternum is not known. 



Appendicular Skeleton. The scapula is relatively smaller than in Doli- 

 chotis and differs somewhat in shape; the coracoid border describes a 

 wider curvature, making the prescapular fossa wider, and the glenoid 

 border is more elevated ; the incisura colli is very long, while the acro- 

 mion has an even greater antero-posterior expansion, but this expansion 

 is less sudden and the posterior process, though nearly as long as in Cavia, 

 is much broader. The coracoid is a well developed, incurved hook, but 

 hardly so prominent as in Dolichotis. 



The pelvis differs from that of Dolichotis in a number of details, as well 

 as in its greater lightness and slenderness of construction. The ilium has 

 a short peduncle, expanding suddenly into the large anterior plate, which 

 is strongly everted ; the prominent acetabular border has a more inferior 

 position than in the existing genus, making the gluteal surface wider and 

 more concave, and the iliac surface, which is more lateral than ventral, is 

 narrower than in the recent genus and the ilio-pectineal process is much 

 more prominent ; the acetabulum is small and subcircular, with projecting 

 border. The ischium, which is much shorter than the ilium, is laterally 

 compressed and has an unusually deep and conspicuous sciatic notch ; the 

 tuberosity is smaller and less prominent than in Dolichotis and the 

 descending process of the ischium is narrower, while the obturator fora- 



