290 



PROCEEDINGS OF THE ACADEMY OF 



[1887. 



and without basal cusps, Avliile the molars have no internal cingula 

 and no opposition of cusps. 



C. (5) Stylodo7itidae\ Thanks to the discoveries of Professor 

 Marsh, this fiimily is now very fully represented and the molar 

 structure is well understood. It embraces Stylodon (Stylacodon)', 

 Aesthenodon, Laodon and Dryolestes which is very similar to the 

 genus Phascolestes (Owen.) There is little doubt therefore that the 

 latter genus belongs here rather than near Peralestes. The resem- 

 blance of Stylodon to Chrysochloris, observed by Professor Owen, is 

 very much strengthened by this extended knowledge of the Stylodon 

 molars, and indicates that this family was insectivorous. The 

 structure of the mandible is very similar to that of Amblotlierium. 



Herbivorous Sub-Group. 



D. The single family embraced in this division is widely separated 

 from all which precede it. The structure of the molars indicates 

 an herbivorous diet similar to that of the Rodents and the Wombats. 



(6) Athrodontidae. Athrodon^ is unique in its dentition among 

 the Mesozoic mammals. The tall trihedral crowns are closely ap- 

 plied at their sides, thus falling into a curve. The inner face is 

 styloid, while the outer is grooved and the triangular wearing 

 surface is traversed by a faint median ridge, thus I'esembling one 

 half the crown of a Phascolomys molar. The last premolar is trans- 

 forming into a molar, the others are small. The canine is large 

 and bifanged. 



The genus Leptodadus is isolated. 



Fig. 3. Tlie inner surface of the left maxilla of Athiodon. 



1. This family name was sutjjgested by Professor Marsh in 1880 to embrace 

 Stylodon and Stylacodon. It is probably equivalent to the Dryolestidae more re- 

 cently proposed by the same author. 



2. These gener.i appear to be the same. 



3. Gen. Nov. Type, maxilla of Stylodon piisillus, Owen. 



