MORRISON MAMMALS: PANTOTHERIA 95 



D. siriatus. Canine smaller than in D. crassus. Possibly a small diastema. P< larger 

 than P:i. Premolar cinguliim with a minute median external cuspule. 



There are so many trivial distinctions between this species and the other three that 

 it may well be valid, although no one of its supposed characteristics can be relied upon 

 as certain and as of definite taxonomic value. Marsh separated it from D. crassus as 

 having a less robust lower jaw, more slender canine, and a small post-canine diastema. 



Dentition 



The canine is a little smaller than in the preceding species, but is otherwise iden- 

 tical. The space back of it is broken and disarranged in the specimen, so that it is not 

 certain whether the supposed small diastema really existed or not. The alveoli clearly 

 indicate six molars, as stated by Marsh, but do not preclude the possible presence of 

 others not yet erupted. 



Mandible 



There are mental foramina beneath Pi and P-. The masseteric fossa is well devel- 

 oped, but not sharply bounded. The coronoid arises at a lower angle than in D. victor 

 or D. strialus, possibly another youthful character. 



Measurements of Type 



Lengths: C Pi P3 P4 Mi M, M, M4 



1.4 I.I 1.3 1.5 .. 2.0 2.0 



Depth of ramus below M4, outside: 3.1 mm. 



Docodon st/perus, new species 



Type. — Y.P.M. No. 10647. Right maxilla with canine and M'". 



Principal Referred Specimens.— Y.P.M. No. 13769. Left maxilla with C, P**, 

 M^"^ and an isolated molar. 



Y.P.M. No. 13770. Right maxilla with P' and M* 



U.S.N.M. No. 2715. Right maxilla with F\ P', and W". 



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



Diagnosis. — A conventional species for upper jaws of this genus. Maximum 

 lengths of first five molars of tj^pe 1.8, 1.9, 2.0, 1.9, 1.6 mm. respectively. 



Dentition 



The canine is a large high tooth, slightly recurved, implanted by two stout roots. 

 The anterior face is convex in contour and is apparently trenchant, but posteriorly 

 there is a concave face, making the tooth triangular in section. 



No specimen indicates the presence of more than three upper premolars. This may 

 indicate that another was late in eruption, as in the lower jaws, but it is more probable 

 that reduction had gone farther than in the lowers and that three was the definitive 

 number. P^ is very small, follows the canine immediately, and has only one root. It 

 has a trenchant but stout main cusp and a small sharp internal cingulum rising to a 



r2-4 



