EDENTATA OF THE SANTA CRUZ BEDS. 349 



prezygapophyses, and a small posterior pair arising from the hinder edge 

 of the transverse processes. 



The humerus (Plate LXIII, figs. 6, 6, No. 15,374) was found isolated 

 and is referred to the present genus because of its resemblance to that of 

 Mylodon and its decided difference from the humeri of the two preceding 

 families. Compared with the humerus of Hapalops, this specimen is 

 strikingly short and heavy and all the processes for muscular and liga- 

 mentous attachment are more prominent; the proximal end is broader, 

 owing to the development of the tuberosities, of which the internal is rela- 

 tively larger and more prominent than in Mylodon, and the bicipital 

 groove is shallow; the shaft is stout; the pectoral ridge is distinct and 

 the deltoid area is much broader than in Hapalops and near the distal end 

 its borders project more prominently; the supinator ridge and external 

 epicondyle are much better developed than in Hapalops and the former 

 has a greater proximo-distal extension than in Mylodon, making the mus- 

 culo-spiral groove very conspicuous ; the internal epicondyle is extremely 

 large and is perforated by the usual large foramen. The trochlea is inter- 

 mediate in character between that of Hapalops and that of Mylodon, dif- 

 fering from the latter in the narrow hemispherical facet for the radius and 

 in the better definition of the groove on the posterior side for the ulna, 

 and from the former in the flatness of the ulnar facet, which is hardly 

 reflected at all upon the dorsal side ; the anconeal fossa is small and 

 shallow. The dimensions of this humerus are as follows : 



Length 160 Distal width over epicondyles 072 



Proximal width 055 " " " trochlea 042 



The radius (Plate LXIII, figs. 7, 8; No. 15,893) is conspicuously short 

 and stout and may be described as intermediate in character between 

 Hapalops and Scelidotherium. The head, which is much damaged, 

 appears to have been discoidal in shape; the bicipital tubercle is very 

 large and rugged and has a slightly more distal position than in Hapalops; 

 the proximal part of the shaft is broader and shorter than in the last named 

 genus, but has a similar shape, while the distal broadening, though more 

 gradual, is much greater, and the external border is more thickened ; the 

 carpal surface is larger in both dimensions and the styloid process is some- 

 what more pronounced. The length of this radius is 123 mm., and its 

 distal width is 30 mm. 



