148 PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



is marked by a large, deep pit, with raised edges and very rough sides ; 

 sometimes there is a small cone at the bottom of the pit, as if for the 

 attachment of a spine or horn. The number of scutes thus marked differs 

 in each species, though perhaps not constantly, but the pits are always 

 present on the two median posterior pairs of plates. In R. petestatns the 

 anterior pair of plates have median bosses, all the others are pitted ; in 

 E. complicatus all the scutes have pits, and in E. crasstis only the two 

 median posterior pairs are so marked, though very small, shallow pits are 

 present in irregular fashion on the others, suggesting that, to a certain 

 extent, the pits were obliterated with advancing age. 



The teeth (Plate XXIV, figs. 9-11) differ quite strikingly in the different 

 species, though nothing is yet known of E. crassus in this respect. In 

 E. petestatns the anterior teeth are remarkably simple and the first 

 upper three are elliptical, while in E. complicatus there is little difference 

 between these teeth and the corresponding ones of Propalceohoplophorus. 

 Both species, however, agree and differ from the last-named genus in the 

 very slight indication of a subdivision of the postero-external lobe on the 

 posterior upper teeth ( 4 ~ a ). 



The skull (Plate XXIX) is very different in its proportions from that 

 of Propalceohophphorus. The cranium is much depressed and very 

 broad, as is particularly well shown in the view of the occiput (fig. 4) ; 

 the forehead is flattened and very wide, extending much more over the 

 orbits than in the last-named genus and ending in much more distinct 

 postorbital processes ; the rostrum is relatively longer and more tapering, 

 but remains broader and more depressed throughout ; the zygomatic arch 

 extends out more widely from the side of the cranium and is broader 

 dorso-ventrally ; the jugal has a much more prominent postorbital process, 

 while the descending suborbital process is relatively shorter; the lach- 

 rymal foramen is smaller and nearer to the edge of the orbit, the anterior 

 rim of which is much more distinctly elevated and flared. 



The mandible, which is known only in E. petestatus, differs notably 

 from that of Propalceohoplophorus ; the symphysis is longer and narrower 

 and the edentulous part of the alveolar border is not everted to such an 

 extent ; the horizontal ramus is relatively shorter and deeper and its ven- 

 tral border is more regularly curved ; the mental foramen is very small, 

 and on the ascending ramus is a deep fossa, which Ameghino regards as 

 a remnant of the alveolar canal ('98, 210). 



