TILLODONTA. 195 



descriptions and figures of its describer. There are three species as- 

 cribed to Tillotherium, while the other genera have two each. The genera 

 are defined as follows: 



' First iuferior incisors present; six inferior molars with cross-crests . . Psittacotherium. 

 First inferior incisors present; ?six inferior molars; trne molars with 



V's Anchippodus. 



First inferior incisors wanting; seven inferior molars; true molars 



with V's Tillotherium. 



The first-named genus approaches most nearly to Calamodon in the 

 structure of the crowns of the molar teeth, and in the shortness of its den- 

 tal series. It is only known from the Puerco formation. The two remain- 

 ing genera have been found in the beds of the Bridger epoch. Tillotherium 

 is nearest to Esthonyx, while Anchippodus is between the former and Psitta- 

 cotherium. 



PSITTACOTHERIUM Cope. 



American Naturalist, 1882, Feb., p. 156 (Jan. 25). 



This genus differs widely from the two genera hitherto known, Anchip- 

 podus and Tillotherium. Owing to the absence of the superior dental series it 

 is not possible to be sure which tooth is the canine. The inferior dental for- 

 mula may be therefore written: I. 2; C. 1; Pm. 3; M. 3; or I. 3; CO; 

 Pm. 3; M. 3; or I. 3 ; C. 1; Pm. 2; M. 3. The first and second incisors 

 iire large and rodent-like, growing from persistent pulps; the second are the 

 larger. The third, or canines, are small and probably not gliriform. There 

 is no diastema. The first premolar (or canine) has a compressed crown 

 with two cusps placed transverely to the jaw axis, and has a comjilete 

 enamel sheath, and probably two roots. The succeeding tooth is also trans- 

 verse, and is two-rooted, judging from the alveolus. The first and second 

 true molars are rooted, and the crown consists of two transverse separated 

 crests, each partially divided into two tubercles. On wearing, the grinding 

 surface of each assumes the form of a letter B with the convexities ante- 

 rior The last iuferior molar is injured. The rami are short, and the sym- 

 physis deep and recurved. 



Two species are known, a larger and a smaller. In both the incisor teeth 

 are very powerful, and the symphysis of the lower jaw is very deep, for 

 their accommodation. They may have been adapted for breaking nuts and 

 .seeds, as well as cutting roots. 



