694 THE WASATCH PERIOD. 



The three genera are distinguished as follows: 



Two superior i^remolars different from true molars Desmatotherium. 



One superior premolar different from true molars; no heel of third inferior molar; nasal 



septum cartilaginous Tapinis. 



Like Tapirus, but nasal septum osseous Elasmognathus. 



CHALICOTHERIID^. 



Gill; Cope, American Naturalist, 1881, p. 340. 



This family had numerous representatives during Eocene time, and a 

 few species of Chalicotherium extended into Miocene time. The boundaries 

 which separate the family from the Lophiodontidce on the one hand and the 

 Menodontidce on the other are not always easy to determine. From the 

 former the symmetrically developed external Vs of the superior molars, and 

 the double Vs of the inferior molars, distinguish it. Yet in Pachynolophus the 

 external Vs are not so well distinguished as in other Chalicotheriidce ; and 

 the anterior cingular cusp produces a part of the asymmetry found in 

 the Lophiodontidce. The character of the double inner cusps of the superior 

 premolars which distinguish the Menodontidce is only applicable to the last 

 premolar in Diplacodqn of the latter, while a trace of the additional cusp of 

 this tooth is found in the Chalicotheroid Nestoritherium. 



In using the following table it must be borne in mind that the number 

 of the toes has been determined in a very few of the genera. Should any 

 of them prove to have but three digits on the anterior foot, such genera 

 must be referred to a new family intermediate between this one and the 

 Paloeotheriidce. 



I. Internal cones of superior molars separate from external lobes. 



A. External tubercles of superior molars separated externally by a conic cusp. 



Fourth inferior premolar like flrst true molar Ectocion. 



AA. External Vs of superior molars separated by an external ridge. 

 a. Incisoi's present. 



/3. No diastema in front of second inferior premolar. 

 Second premolar without inner lobe; last molar with one inner cone.. .Leurocephalus. 

 Second premolar with inner cone; last superior molar with one inner cone. . Palceosyops. 

 Second premolar with inner cone ; last superior molar with two inner cones . . Limnohyus. 

 /5/3. A diastema in front of second inferior premolar. 



Two inner cones of last superior mola v , . Lambdotherium, 



aa. Incisors absent from both jaws. 

 Last superior molar with one internal cone Nestoritherium. 



II. One or both internal cusps of superior molars united with the external lobes by 



cross-crests. 



