EDENTATA OF THE SANTA CRUZ BEDS. 355 



- is of compressed elliptical section and of remarkably small size, while 

 -~- are of unusually well-defined triangular form, and A is less distinctly 

 so. The two series of upper teeth diverge anteriorly in only a moderate 

 degree, while in the palate above mentioned the divergence is much more 

 decided and - is large and 'triangular. In the mandibular dentition there 

 is considerable difference between the types of A. profimdatum and A. 

 acitleatwn, and even on the opposite sides of the same jaw. In the former 

 2 is more cylindrical and -3 more antero-posteriorly compressed, while in 

 the latter 2 is more triangular and T has a remarkably broad posterior 

 lobe ; in both T is of compressed elliptical section and has a large, 

 deeply notched surface of abrasion on the hinder face. 



The skull, as displayed in the type of A. aculeatum, is very elongate 

 and quite broad posteriorly, the cranium reaching its maximum width at 

 the glenoid cavity, and thence narrowing to the interorbital region, while 

 the face is very slender, though the rostrum broadens somewhat anteriorly. 

 The occiput is low and the upper contour of the skull, which rises but 

 little to the parietal eminence, has a nearly horizontal and slightly sin- 

 uous course. The basioccipital and basisphenoid are very broad ; the con- 

 dyles are quite small and are separated ventrally by a wide and deep 

 notch. The preorbital region is somewhat longer than in any other spe- 

 cies ; the palate is very narrow and quite strongly convex behind, widen- 

 ing and flattening anteriorly, and is continued for a short distance behind 

 the last tooth ; the median notch for the premaxillary spines is a deep and 

 harrow V. The posterior nares follow the shape of the cranium, being 

 very broad behind, contracting forward and becoming very narrow at the 

 front border. The mandible is best shown in the type of the species, in 

 which it differs in a number of respects from that of N. angulatum ; the 

 coronoid is more recurved and inclined ; the condyle is placed upon a 

 longer neck and is more raised above the level of the teeth, while the 

 angular process appears to have been much longer. In the type of A. 

 aculeatum, the predental beak has more nearly parallel sides and an 

 elevated dorsal border. 



In the following table No. i is the type of Ammotherium profundatum, 

 No. 2 the palate referred to the same species, and No. 3 the type of A. 

 acttleatum, all in the Ameghino collection. 



