94 AMERICAN MESOZOIC MAMMALIA 



below the internal groove, a fact which suggested the specific name. This resembles the 

 similar condition in the bone of most very young mammals and no doubt is due to the 

 same cause. 



Lengths: C P^ Pg 



ca. 1.3 i.o 0.8 

 Depth of ramus below M4, inside: 3.9 mm. 



Docodon crassus (Marsh 1887) 

 1887. Enneodon crassus. Marsh, Amer. Jour. Set. (3) XXXIII, 339. 

 1889. Ennacodon {crassus), Marsh, Additional genera, etc., 15. 



Type. — U.S.N.M. No. 2130. Right lower jaw in matrix, outer aspect, with C, 

 P3-4, and M1.4. Fig'd (as Enneodon crassus). Marsh 1887, PI. X, fig. 4. 



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



Diagnosis. — Cheek teeth apparently P3 Me, but probably P4 M7-8 in adult. Jaw 

 shorter and more shallow, but this probably also due to youth. Mi apparently larger 

 than in D. victor or D. striatus and posteroexternal premolar cingula less developed, 

 ending weakly and indefinitely anteriorly. P3 = P4. 



Dentition 



Save for the details mentioned in the diagnosis, the dentition is like that of D. 

 victor or D. striatus. The posterior portion of the jaw is now so broken that it cannot be 

 restored, but according to Marsh there were alveoli for two additional molars, making 

 six. But there is no assurance that more were not still enclosed in their crypts. 



Mandible 



Except for its youth and the crushing which it has suffered, the mandible does not 

 differ in the known parts from that of the preceding species. 



Measurements of Type 



Lengths: C P3 P4 Mi M2 M3 M4 



1.6 1.4 1.4 1.8 1.9 2.0 2.1 

 Depth of ramus below M4, outside : 3.2 mm. 



Docodon a ffinis {M.aTsh 1887) 



1887. Enneodon affi-nis. Marsh, Amer. Jour. Sci. (3) XXXIII, 339. 

 1889. Ennacodon {affinis). Marsh, Additional genera, etc., 15. 



Type. — U.S.N.M. No. 2129. Left lower jaw in matrix, outer aspect, with C, Pi, 



P3-4, and M2-4. 



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



Diagnosis. — Cheek teeth apparently P3 Me, but individual probably immature. 

 Proportions of jaw nearly as in D. crassus. Mi apparently larger than in D. victor or 



