226 



PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



only the last rib lacks the tubercle entirely. Seen from the side, the 

 longer ribs display a double curvature, somewhat as in Cholczpus, though 

 in a less marked degree. 



The sternal ribs are thin and blade-like, antero-posteriorly compressed, 

 and with principal diameter directed dorso-ventrally ; the distal end bears 

 a facet for the body of the mesosternal segment, and a rounded, tubercle- 

 like projection for the ventral process of the segment. 



The sternum is imperfectly known and it is not possible to determine 

 the number of segments of which it is composed. The manubrium, which 

 bears considerable resemblance to that of Cholczpiis, is of cruciform shape, 

 with long, narrow anterior projection ; the body of the presternum is 

 broad, deeply concave on the dorsal side, and with narrow, elongate and 

 saddle-shaped facets for the first pair of ribs ; the posterior end is narrowed 

 and has a smooth surface for the first segment of the mesosternum ; this 

 surface presents obliquely upward and backward. The segments of the 

 mesosternum resemble those of Mylodon, as is true of all the Santa Cruz 

 Gravigrada in which this structure is known. Each segment consists of 

 a flat, depressed plate, with slightly concave anterior and convex posterior 

 faces, and at the angles are facets for the heads of the sternal ribs ; from the 

 ventral side of the plate arises a very large, club-shaped process, with 

 constricted neck, which carries four concave facets for the tubercles of the 

 sternal ribs ; except for these facets, the surface of the process is every- 

 where rugose. No specimen containing the xiphisternum has yet been 

 found. 



The following measurements of the vertebrae are from No. 15,545, except 

 those of the lumbar vertebrae, which are taken from No. 15,011. 



MEASUREMENTS. 



Neck, length 140 



Thorax, length (following curve). ..... .416 



Loins, length 099 



Sacrum, length 115 



Atlas, length 030 



width 050 



dorso-ventral height 0265 



Ax s, length of centrum 025 



width of anterior face 029 



" " posterior face 013 



" " neural spine 026 



Third cervical, length of centrum 



" " width of anterior face . . . 



" " " " posterior face . . 

 Fourth cervical, length of centrum 



" " width of anterior face . . 



" " " " posterior face. 

 First thoracic, length of centrum 



" " width of anterior face . . . 



" " " " posterior face . . 

 First thoracic, width over transverse pro- 

 cesses 



,018 



.0125 



.014 



.017 



.013 



.014 



.018 



.014 



.017 



.050 



