MORRISON MAMMALS: TRICONODONTA 



35 



PR/Aconnu 



Fig. II. Pruuodon. Diagrammatic internal view of right lower jaw. 

 Three times natural size. 



Osborn (i888a, p. 

 229) questioned the right 

 of this form to generic 

 separation from Tricono- 

 doti. He suggested that 

 the tj-pe (of Priacodon 

 jerox) might be immature, 

 with a deciduous tooth in 

 place. The present writer 

 (Simpson 1925B, p. 160) 

 concluded that this was 

 not the case. These find- 

 ings have since been care- 

 fully compared with those from the pertinent European material and are fully con- 

 firmed. From these comparisons, from the several lower jaws now referred to Priaco- 

 don, and from the upper jaws which clearly have three premolars and four molars, 

 there can be little doubt that the definitive formula of Priacodon is P| M^ and that the 

 genus is distinct from either Triconodon or Trioracodon, although closely related to 

 both. 



Priacodon ferox (JAzx^h. 1880) 



1880. Tinodon ferox. Marsh, Amer. Jour. Set. (3) XX, 236. 



1887. Priacodon jerox, Marsh, Amer. Jour. Set. (3) XXXIII, 341. 



1888. Priacodon {Triconodon?) ferox, Osborn, Jour. Acad. Nat. Sci. Phila., IX, 229. 

 1898. Triconodon ferox Owen, Trouessart, Cat. Mam., 1250. (Error.) 



Type.— Y.P.M. No. 606. Right 

 lower jaw in matrix, inner aspect, with 

 Pi-3, Mi-3 and alveoli for other teeth. 



Referred Specimen. — Y.P.M. 

 No. 13626. Right maxilla, nearly com- 

 plete, with crowns of M1.3. 



Horizon and Locality. — Morri- 

 son formation, Quarry 9, Como Bluff, 

 Wyoming. 



Diagnosis. — M3 longer than M2 

 and with strong posterior cingulum 

 cusp. Pi = P2. P2 with no anterior 

 cusp, low central cusp, faint cingulum. 

 In upper jaw (referred), lengths of 

 first three molars about 2.0, 2.6, and 

 2.7 respectively; a broad palatal 

 groove internal to raised molar bor- 

 der; upper molars with sharp continu- 



m2 ml 



Tn3 1112 ml 



f 



ml 



D 



Fig. 12. Occlusion in triconodonts. A. On the hypothesis 

 that cusp b below occludes between a and b above. B. 

 The correct relationships, with b below fitting between 

 the teeth above. C. Section through the center of a 

 lower cusp in occlusion, showing how the tip scrapes 

 upward and inward while shearing against the upper 

 molar. D. Somewhat schematic view of left molar series 

 from the outside, showing the relationships of the cusps 

 of the lower molars to the notches in the crests of the 

 upper molars. (After Simpson, 1925B.) 



