26 AMERICAN MESOZOIC MAMMALIA 



Psalodon potens (Marsh 1887) 



1887. Ctenacodon fotens, Marsh, Amer. Jour. Set. (3) XXXIII, 333. 

 1927. Psalodon fotens, Simpson, Amer. Jour. Set. (5) XIV, 38. 



Type.— Cat. No. 11834, Y.P.M. Right upper jaw with V". Fig'd, Marsh 1887, 

 PL VIII, figs. 2-3. 



Referred Specimens. — Y.P.M. No. 10363. U.S.N.M. No. 2680. Am. Mus. Nat. 

 Hist. No. 3003. These add nothing to our knowledge of the species. 



Diagnosis. — Upper cheek teeth with the characters of the genus. Length P^"® 

 ca.%.% mm. 



Dentition 



P^"" are essentially similar to the corresponding teeth of Ctenacodon laticefs save 

 in size. They were preserved in the matrix anterior to the preserved bone and the crum- 

 bling of the matrix has dissociated them from the rest of the specimen, making it im- 

 possible to verify the original arrangement, but Marsh's figure shows them to be 

 oriented as in Ctenacodon (his Allodoti). P* differs markedly from the latter genus, 

 however. The posterointernal cusp is very large, constituting almost the entire crown, 

 and the anterointernal cusp is much smaller, while the external cusp is smaller still — 

 a mere projection on the confluent slopes of the other two. It is also more anterior in 

 position than in the preceding teeth." 



P* consists essentially of four cusps in a single row, the anterior one a little the 

 smallest. These form a shearing edge and the internal slope is abraded. On the outer 

 slope there are three very small and apparently quite functionless cuspules. P® is simi- 

 lar, with four cusps forming a sharp shearing edge, the posterior one a little the small- 

 est. On this tooth the outer cusps are still less prominent, but a single cusp-like vestige 

 on the anteroexternal part of the crown occurring. 



Measurements 

 Lengths : 



pl-5 pi p2 p3 p4 p5 



Y.P.M. 11834 8.8 1.4 1.5 1.7 2.2 2.0 



Y.P.M. 10363 .. 1.3 .. 1.7 2.1 



Psalodon for tis (Marsh 1887) 



1887. Allodon fortis, Marsh, Amer. Jour. Sci. (3) XXXIII, 331. 

 1927. Psalodon fortis, Simpson, Amer. Jour. Sci. (5) XIV, 38. 



Type. — Cat. No. 11760, Y.P.M. Right premaxilla with P'' and alveolus for V. 

 Fig'd, Marsh 1887, PI. VII, figs. 7-10. 



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



^^ The apparent fourth cusp posterior to the main one in Marsh's woodcut is merely a shoulder on 

 the largest cusp and not a distinct projection. 



