MESODONTA. 215 



The skeleton of the New Mexican form includes an entocuneiform, 

 like that of Stypolophus Mans, which indicates a non-opposable hallux. 



It is apparent that the supposed Lemurine Mammalia of the type of 

 Tomitherium, which have the formula of the molar teeth 4-3, cannot be 

 separated by ordinal distinction from the Creodonta. They differ from them, 

 it is true, in their wholly tubercular molar teeth, but in this relate to them 

 as the Bears and Procyonidoi do to other Carnivora. I have, therefore, pro- 

 posed* to constitute these a distinct group or suborder, intermediate in 

 position between the Creodonta and the Prosimice, under the name of the 

 Mesodonta. I cannot now find characters by which to distinguish this divis- 

 ion from the Insectivora as an order. 



In my report to Dr. Hayden on the paleontology of the Bridger Eocene 

 of "Wyoming.t I included six species, viz, Tomitherium rostratum, Pantolestes 

 longicaudus, Sarcolemur furcatus, S.pygmceus, Hyopsodus vicarius, and H. pauliis 

 Leidy, which belong to this suborder. As many species of Mesodonta 

 referred to various orders are described by Dr. liCidy in his quarto report 

 in the same series. In my report to Lieutenant Wheeler on the Vertebrata 

 of the Eocene of New Mexico obtained by the expedition of 1874, eleven 

 species are included, none of which had been certainly obtained from the 

 Bridger beds. 



A synopsis of the genera is given below, in which the characters are 

 derived from the dentition of the lower jaw, the pai-t usually preserved. 

 While considerable variety is to be observed in the structure of the teeth, 

 they furnish also close approximations, so that their discrimination requires 

 careful scrutiny. 



The genus Anaptomorphus Cope, although included in the synopsis, 



probably belongs to the Prosimice. 



I. Last true molar with cusps in opposing pairs. 



A. Anterior inner cusps, two or a double one, on some of the molars. 



* Three premolars. 



"Last premolar without inner tubercle" (Leidy), like the other 



premolars Omomys. 



Last premolar with inner tubercle like the molars Microsyops. 



• * Four premolars ; last molar heeled. 



Last premolar without inner tubercle; premolars two-rooted.. Pantofes<es. 



• Proceed. Acad. Phila. , 1876, p. 88. Report U. S. Geol. Surv. West of 100th Mer., iv, p. 80, 1877. 

 t Annual Report U. S. Geol. Surv. Terrs, for 1872, 1873, pp. 546, 607. 



