4 PROCEEDINGS OF THE NATIONAL, MUSEUM vol. 82, art. 2 



but not molariform, upper molars low-crowned, basically tri- 

 tubercular but with large posterointernal heel, cusps high and sharp, 

 protostyle small or absent, molars less transverse than in Conacodon 

 or Ilaploconus.^ It is not closer to any other genus and differs 

 no more from other species referred to Ardsonchus than they differ 

 between themselves. In short, surprising as is the discovery of an 

 Anisonchns at this place and level, the generic reference is not open 

 to question. 



Two valid species of Anisonchus have previously been established : 

 A. gillianus from the Puerco, and A. sectorius (the type) from the 

 Torrejon. The genus also occurs in the Fort Union, but the species 

 there present have not yet been defined or identified. A. gillianus 

 and A. sectorius are very distinct, and A. fortunatus is also a very 

 clear-cut species. In part it combines characters of the other two. 

 Thus the strong internal projection of the hypocone base and the 

 shape and proportions of the premolars are more like A. gillianus, 

 while the molar size and overall proportions, separation of paracone 

 and metacone, and reduction of protostyle are more like A. secto- 

 rius. Other characters, such as the very large hypocones and ex- 

 treme compression of trigons, are distinctive from either species. 

 The combination of these various characters is unique. 



Being about equally distinct from A. gillianus and A. sectorius 

 its closer affinities are in doubt. It is perhaps in a stage of evolu- 

 tion analogous to that of A. sectorius but derived independently 

 from a more primitive, more A. gillianus -like common ancestry. 



The age of the specimen is surely Paleocene. Other specimens of 

 this genus are loiown only from the Lower and Middle Paleocene, 

 and A. fortunatus is not apparently more advanced than those from 

 the latter. More exactlj^, but with somewhat less security, it seems 

 to be of approximately Middle Paleocene, Torrejon age. 



The discovery of mammal-bearing Paleocene sediments nearly 

 half a mile below the surface in Louisiana (and far below sea level) 

 is a very extraordinary and interesting fact, but unfortunately it 

 can hardly be said to open up a new field for collecting. 



- Absence of conules is sometimes given as characteristic of Anisonchus or the Ani- 

 sonchinae, but the less-worn specimens of both San Juan Basin species of Anisonchus 

 show small but distinct conules, although less developed than in the present specimen. 



U. S. GOVERNMENT PRINTING OFFICE: 1932 



