86 AMERICAN MESOZOIC MAMMALIA 



Marsh described three genera, Di-plocyiwdon = Dicrocynodon = Diacynodon, 

 Docodon, and Enneodon = Ennacodon. If valid, these would now be called Dicrocy- 

 nodon, Docodon, and Ennacodon, and they have generally been accepted under these 

 names. In his former studies (e.g., 1927B, p. 415-6) the present writer has followed 

 custom in recognizing all three genera, although he has already pointed out that they 

 are almost surely synonymous. He now feels, however, that this practice cannot reason- 

 ably be continued. As will immediately be shown, separation of the genera cannot be 

 maintained and the continued recognition of all three names, even provisionally, 

 would perpetuate an incorrect name not only for the most characteristic and perfect 

 specimens but also as the name of this peculiar and important family. The step was 

 not previously taken because of reluctance to modify nomenclature so long established, 

 but the change appears to be inevitable and can better be made in the present detailed 

 revision than in some future and possibly more obscure paper. 



Docodon Marsh 1881 



1880. Diflocynodon, Marsh, Amer. Jour. Sci. (3) XX, 235. Non Diplocynodon, Pomel, 1846. 



1881. Docodon, Marsh, Amer. Jour. Sci. (3) XXI, 512. 



1887. Enneodon, Marsh, Amer. Jour. Sci. (3) XXXIII, 339. Non Enneodon, Heckel, 1853, 

 non Enneodon Prangner, 1845. 



1888. Dicrocynodon, Marsh in Osborn, Jour. Acad. Nat. Sci. Phila. (2) IX, 263. To replace 

 Di-plocynodon, preoccupied. 



1890. Ennacodon, Marsh, Additional genera, etc., 15. To replace Enneodon, preoccupied. 

 1890. Diacynodon, Schlosser, Biolog. Centralbl., X, 242. To replace Diflocynodon, preoccupied. 

 Antedated by Dicrocynodon. 



Definition. — Dental formula 1 3+ Cj P3.4 M^tg. Lower molars subquadrate. 

 Trigonid about as wide as talonid ; in addition to main external cusp with a prominent 

 anteroexternal cusp, two well-developed internal cusps, and low anterointernal basined 

 cingulum. 



Type. — Docodon striatus Marsh. 



Types of Synonyms. — Dicrocynodon victor (Marsh). Ennacodon crassus 

 (Marsh). 



Distribution. — Morrison formation, Wyoming and Colorado. 



This genus is usually referred to in recent texts and papers as Diflocynodon or 

 Dicrocynodon. There is no justification for the continued use of the former name, 

 which properly belongs to a well-known genus of Crocodilia. Dicrocynodon is not pre- 

 occupied, but evidence is here adduced to show that this name is synonymous with the 

 earlier Docodon. 



In defining Docodon, the only generic difference from "Diflocynodon" given by 

 Marsh was that it had but seven molars, while "Diflocynodon" had eight. The dental 

 foramen was supposed to be farther forward, but other characters were admitted to be 

 in close agreement. Close simultaneous comparison of the two types, both of which are 

 excellent specimens, confirms the difference in molar number, but fails to reveal any 



