MORRISON MAMMALS: MULTITUBERCULATA 27 



Diagnosis. — A large prcmaxilla probably belonging to Psalodon fotetis and not 

 directly comparable with any other American material. Differs from Bolodon espe- 

 cially in the simple 1', resembling I* save in size. 



Dentition 



r was very small, closely appressed to the equivalent tooth of the opposite side, 

 and directed more forward than downward. I", on the contrary, is much enlarged. The 

 root is long and large, but must have been closed in the adult as the crown is definitely 

 delimited and is not very long. The tooth is inclined at about 60° from the horizontal. 

 The anterior and lateral faces of the crown are not distinguished from one another and 

 are convex, with faint longitudinal flutings. The median face is nearly plane and was 

 apparently in contact with V of the opposite side. This face is separated from the pos- 

 terolateral face by a marked angulation, on which the wear chiefly occurs. Above the 

 facet of wear and slightly external to it is a small accessory cusp. The posterolateral 

 face is small, lies below this cusp, and is distinctly concave. 



P is about half as large as V and nearly parallel to it. The tip is rounded, sub- 

 spatulate, and there is a very small accessory cusp. There is evidence of wear similar 

 to that on I". The lower incisors probably could work against either I" or I ^ at will. 



Skull 

 The nares open terminally just above the anterior incisors and are small. The 

 anterior palatine foramen is large and is at the extreme anterior end of the palate just 

 internal to V. The premaxilla is a triangular bone of moderate size. Its suture with 

 the maxilla, in the lower part at least, is very steep. 



('Psalodon marshi, new species 



Type. U.S.N.M. No. 2684. Crushed and broken left lower jaw with the incisor, 



P,.4. and Ml. Fig'd, Marsh 1887, PI. VIII, figs. 7-9. 



Principal Referred Specimens.— U.S.N.M. No. 2687. Broken lower jaw with 



1, P2.4, and Ml. 



U.S.N.M. 2690. P2-4. 



Y.P.M. No. 13669. Isolated P,. 



U.S.N.M. 2679. Isolated broken lower incisor. Fig'd, Marsh 1887, PI. VII, figs. 



14-15. 



Horizon and Locality.— Morrison formation, Quarry 9, Como Bluff, Wyoming. 



Diagnosis.— Lower jaws and teeth possibly belonging to Psalodon fotens. Length 

 Pi-4, ca. 6.5 mm. 



In addition to its larger size. Marsh considered the lower M2 and more perpen- 

 dicular coronoid as distinguishing these jaws from Ctenacodon serratus. The size 

 alone is sufficient to indicate such specific distinction, but the other characters cited by 

 Marsh appear to be due to crushing. It is not possible at present to point to any generic 

 distinctions between ^.Psalodon marshi and Ctenacodon serratus, but it is more than 



