MORRISON MAMMALS: PANTOTHERIA 93 



Docodon strlatus Marsh 1 88 i 

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



Type. — Y.P.M. No. 11823. Right lower jaw in matrix, internal aspect, with C, 

 ?,.,, and M,..v Fig'd. Marsh 1887, PI. X, fig. 2. 



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



Diagnosis. — Cheek teeth apparently P^ M7. M7 slightly smaller than that of D. 

 victor. Mi-o slightly smaller and jaw longer and stouter than in D. crassus or D. 

 affinis. 



Dentition 

 The whole dentition is hardly distinguishable from that of D. victor. P1.2 seem 

 slightly larger, but they are worn in the type of D. victor. The internal cingula on P3-4 

 are slightly straighter, but the difference might be individual. The molars, so far as 

 preserved, agree in every detail. Mb, preserved in both, is of the same size. Judging 

 from alveoli, this was also true of Ms, but M7 was smaller in the present species. Dis- 

 section of the jaw seems to indicate that there was no Ms, even when adult, a point 

 which has been sufficiently discussed above. 



Mandible 



The internal features of the mandible are also like those of D. victor, but they are 

 here more clearly displayed. The symphysis is unusually long, ending beneath the 

 first or second molar. The condyle was broken off (previous to the preparation of the 

 earliest figure) and refixed at a slightly incorrect angle, so that at first sight it appears 

 quite different from that of D. victor, but this was not original. From the condyle there 

 runs forward a ridge which is very high and sharp just anterior to the neck of the 

 condylar process and above the posterior end of the angle. It here has its outer edge 

 turned upward, undoubtedly for the attachment of one or both of the pterygoid mus- 

 cles. Anterior to this it becomes lower and more rounded and passes into the alveolar 

 border behind the last molar. Beneath this ridge and debouching posteriorly at the 

 upper part of the condylo-angular notch there is a wide and deep groove. It becomes 

 more shallow, without narrowing, as it passes forward, and then becomes deeper again 

 and communicates with the dental foramen. Below this groove is a ridge which runs 

 forward and passes into the lower part of the alveolar portion of the mandible, and 

 below this is the somewhat convex inner surface of the efflected angle. 



Anteriorly the internal groove is a normal, narrow, rather deep sulcus, nearly 

 reaching the symphysis and diverging slowly from the lower border and broadening 

 as one follows it posteriorly. Beneath the anterior end of M7 it branches, the upper 

 narrower branch running back to a point just anterior to the dental foramen, and the 

 lower broader main branch passing onto the ridge immediately above the angle, where 

 it becomes shallower and disappears at a point considerably posterior to the dental 

 foramen and below it. 



The bone of the horizontal ramus is marked by numerous striations above and 



