54 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
The tail was probably long and heavy, but its exact length cannot be 
determined from the material available. The most complete specimen has 
sixteen free caudals in series (PI. IX). The proximal caudals (PI. VI, 
figs. 1 6, 17) have robust transverse processes, which decrease in length 
and increase in antero-posterior diameter posteriorly. These soon bifur- 
cate, forming a process at either extremity of the elongated, hour-glass- 
shaped centrum (PI. VI, figs. 18-20). The neural arch disappears at 
about the tenth caudal, a pair of processes at the anterior and posterior 
extremities of the centrum alone remaining. Chevrons are present (PI. 
IX). 
In proportion to the size of the animal, the ribs (PI. IX) are quite 
robust, the first rib exceeding in width that of Protypotherium. It is 
broadly expanded antero-posteriorly at the proximal and distal ends. 
Farther back in the series the ribs are cylindrical. 
The sternum is imperfectly known, as but three segments are present in 
the most complete specimen (No. 15,401). The first segment (PI. VI, fig. 
21) is dagger-shaped, with its anterior half, corresponding to the blade of 
the dagger, sharply keeled inferiorly. The two mesosternal segments 
preserved are hour-glass-shaped and doubly keeled inferiorly, the keels 
diverging anteriorly and posteriorly. 
Appendicular Skeleton. — The scapula (Pis. VI, fig. 13; VIII, fig. 8) 
varies somewhat in shape with the species, but it is quite probable that a 
part of the difference is due to crushing. In all the specimens the cora- 
coid border is strongly convex, the convexity continuing unbroken over 
the vertebral border as far as the inferior angle, which is quite prominent. 
The axillary border is convex in /. robustum and concave with elevated 
margin in a specimen referred to I. extensum (No. 15,041), but this may 
be due to crushing. Some slight differences in the shape of the coracoid 
border exist, but these can be more readily appreciated after an examina- 
tion of the accompanying figures (Pis. VI, fig. 13 ; VIII, fig. 8) than 
from a description, however detailed. The surface of the supraspinous 
fossa is slightly undulatory in /. robustum and strongly convex in I. ex- 
tensum , but just how much of the convexity is due to crushing is hard to 
determine. The infraspinous fossa is concave transversely in both species, 
but more so in the one last mentioned. The spine is high, with narrow, 
flattened crest and short metacromion. The neck is short and thick. 
The glenoid cavity is elliptical in outline, concave in all diameters, and 
