EDENTATA OF THE SANTA CRUZ BEDS. 



is large and has very prominent borders, but the very large sulcus for 

 the round ligament reduces the articular surface to a comparatively narrow 

 band. 



( 1 1 ) The limb-bones are, to a certain extent, intermediate in their pro- 

 portions between those of the Pleistocene Gravigrada and those of Myrme- 

 cophaga, being relatively shorter and heavier than in the latter, more 

 elongate and slender than in the former, among which Megalonyx and 

 Nothrotherium have limb-bones most resembling those of the Santa Cruz 

 types. There are also many points of resemblance to the corresponding 

 parts of the existing Tardigrada. 



b -'c 



FIG. 22. 



Humeri of Santa Cruz Gravigrada, x \. a, Hapalops longiceps ; b, H. ruetimeyeri ; c, Pele- 

 cyodon arcuatus ; d, ? Nematherium sp. 



(12) The humerus is very constant in its characters among the Santa 

 Cruz representatives of all three families and is very similar to that of 

 Megalonyx and Nothrotherium. The head is small and sessile, the tuber- 

 osities are of subequal size, the shaft elongate, subcylindrical and slender, 

 except at the distal end, the deltoid area very large and prominent ; the 

 distal end is much expanded and antero-posteriorly compressed, and bears 

 a very prominent epicondyle and supinator ridge ; the entepicondylar fora- 

 men is invariably present, while in all the Pleistocene genera, except 

 Nothrotherium, this foramen is absent. The humerus attributed to the 

 Santa Cruz Mylodontidce differs only in being somewhat shorter and 

 stouter. 



(13) The ulna has a rather stout, laterally compressed shaft, tapering 

 to the distal end and with distinct sigmoid curvature ; the olecranon is 

 quite small and straight, without transverse expansion. 



