EDENTATA OF THE SANTA CRUZ BEDS. 267 



a certain extent, Hyperleptus may be regarded as intermediate between 

 the two genera named, but its peculiar premaxillaries show that it does 

 not form a member of the same series, but is an offshoot from that series. 

 As regards the connection between Eucholccops and the Pleistocene gen- 

 era, Lydekker has made the following suggestion ('94, 98). "The genus, 

 which is evidently a generalized one, is nearly allied to the ancestral 

 stock of both Mylodon and Megalonyx, if indeed it be not the actual pro- 

 genitor of both." With this suggestion I am unable to agree. Euckolccofis 

 is in all respects a typical member of the Megalonycttida and is no more 

 nearly related to Mylodon than is any other Santa Cruz representative of 

 this family. As will be shown in a later section, genera much more 

 closely allied to the direct ancestor of Mylodon are known in the Santa 

 Cruz fauna, as is also the very probable "actual progenitor" of Megalonyx. 

 Eucholceops, on the contrary, is almost certainly the final term of a series 

 which because extinct at the close of the Santa Cruz epoch. On the 

 other hand, it is undoubtedly true that in Santa Cruz times the three 

 families of the Gravigrada were much less widely separated than they had 

 become, through divergent evolution, in the Pleistocene, and, in that sense, 

 Eucholocops is " nearly allied to the ancestral stock of both Mylodon and 

 Megalonyx" but not more so, it may be added, than to that of Megatherium. 



EUCHOLOEOPS INGENS Ameghino. 



(Plate LVII, Figs. 2, 2", 3.) 



Eucholaops ingens Amegh. ; Enumeracion sistematica, etc.; 1887, p. 21. 

 Eucholaops latirostris Amegh.; Rev. Argent, de Hist. Nat. ; T. I, 1891, 

 p. 322. 



This, the type-species, is the largest and most massive of the genus, 

 though there is much individual variation in regard to size. In the males, 

 at least, the caniniform teeth are very large, of triangular section and 

 worn by abrasion to a sharp point. The mandible has a short horizontal 

 ramus, which is remarkable for its depth and thickness and for the con- 

 vexity of its ventral border, that of the ascending ramus being concave 

 and at a much higher level, except for the downward curvature of the 

 angular process, which is unusually broad. 



In the collection of the American Museum of Natural History is a 

 mandible (No. 9,307) which probably pertained to a female of this species 

 and is considerably smaller than the robust animals with large caniniform 



