EDENTATA OF THE SANTA CRUZ BEDS. 329 



Although the difference is not at all radical, no other contemporary genus 

 has such teeth and they may be recognized at a glance. 



Hardly anything is known of the skull, merely the palate and most of 

 the mandible ; the former resembles that of Planops in being nearly flat, 

 but differs in a decided tendency to assume the triangular form. The 

 mandible has a long and broad predental beak and the ventral border of 

 the horizontal ramus, which in P. filholi is but moderately convex, in P. 

 moyani is so much arched downward as to have a notable resemblance to 

 the jaw of Megatherium. The skeleton is very imperfectly known and 

 only in association with one species, P. potens, and will be described 

 under the heading of that species. In brief, it may be said that the 

 known parts of the skeleton generally agree quite well with the corre- 

 sponding parts of the Santa Cruz Megalonychidce, but there are several 

 significant differences, which are suggestive of a relationship with the 

 Megatheriidcz. It can hardly be maintained, however, that any of the 

 latter family were directly derived from any known species of Prepotherium. 



PREPOTHERIUM FILHOLI Ameghino. 



(Plate LIX, Figs. 2, 2".) 



Prepotheritim filholi Amegh. ; Rev. Argent, de Hist. Nat, T. I, 1891, 

 p. 158. 



In addition to the type specimen in the Ameghino collection we have 

 in the Brown collection of the American Museum of Natural History a 

 right ramus mandibuli (No. 9,573), which appears to be referable to the 

 present species. 



The upper caniniform, -, is small, erect, cylindrical and horizontally 

 worn, and the molariform teeth are characterized by their transverse width 

 and great antero-posterior compression ; the transverse crests are parallel, 

 but the angles of the teeth are so rounded as to give the grinding surface 

 a compressed oval, rather than a rectangular shape ; - and ^ are of nearly 

 equal size, - and - progressively smaller. The lower dentition differs 

 slightly from the upper ; T, which is implanted behind the end of the sym- 

 physis and is followed by a short diastema, is small and very slightly com- 

 pressed laterally ; * and ? are transversely oval, but less compressed antero- 

 posteriorly than the upper teeth ; \ is also transverse, but with a tendency 

 to the subcylindrical shape. 



