MORRISON MAMMALS: MULTITUBERCULATA 



21 



Ctenacodon laticeps (Marsh 1 88 1 ) 



1881. AUodon laticefs. Marsh, Amer. Jour. Set. (3) XXI, 511. 

 1927. Ctenacodon laticeps, Simpson, Amer. Jour. Set. (5) XIV, 37. 



Type.— Cat. No. 11 761, Y.P.M. Part of left maxilla with ?'" and M''. Fig'd, 

 Marsh 1887. PI. VII. figs. 1-2. 



Prin'cipal REFERREn SPECIMENS. — U.S.N.M. No. 2681. Part of left maxilla 

 with P* ^ Fig'd, Marsh 1887, PI. VII, figs. 3-4. 



U.S.N.M. No. 2682. Part of left maxilla with P*' and M\ Fig'd, Marsh 1887, 

 PI. VI I, figs. 5-6. 



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

 ming. 



Diagnosis. — Based on upper jaws possibly belonging to Ctenacodon serraius, and 

 including all the upper jaws probably referable to Ctenacodon. Length of premolar 

 series about 4.5 mm. 



The genus AUodon was originally 

 founded on its possession of five premolars, 

 supposedly distinguishing it from Ctenaco- 

 don with only four lower premolars. In 

 1887 Marsh recognized the weak point of 

 this definition and inferred that AUodon 

 had only four lower premolars, like Ctena- 

 codon. At this time he also founded a sec- 

 ond species of the supposed genus, AUodon 

 fortis "three or four times as large as AUo- 

 don laticeps." This second species was 

 based on a premaxilla, and had no parts 

 which could be directly compared with the 

 genotj-pe. Its reference to the supposed 

 genus was therefore entirely by inference, 

 the basis for which is not now clear. From 

 the character of 1* in this premaxilla he in- 

 ferred that the lower incisor must be gliri- 

 form, with a chisel-like end, and he figured 

 an isolated tooth supposed to show this 

 character. This was supposed to substanti- 

 ate the difference between AUodon and 

 Ctenacodon. The weakness of this position 

 is apparent from the standpoint of present 

 work although, historically considered, 

 Marsh's course was much nearer the truth 

 than that of many later workers. In the 

 first place, there was no real evidence that 



YPMii/ti 



Fig. 6. Upper premolars of American plagiau- 

 lacids. A, Psalodon potens, type, right upper 

 jaw. AS internal. A-, external. A", crown. B, 

 Ctenacodon laticeps, type, left upper jaw. B', 

 internal. BS external. B^, crown. A, 7J/2 times 

 natural size. B, 12^^ times natural size. 



iC&^4^ 



