90 AMERICAN MESOZOIC MAMMALIA 



Docodon victor {M.avsh. iSSo) 



1880. Diflocynodon victor. Marsh, Amer. Jour. Sci. (3) XX, 235. 



1888. Dicrocynodon {victor), Marsh in Osborn, Jour. Ac. Nat. Sci. Phila., IX, 263. 



Type. — Y.P.M. No. 11826. Right lower jaw nearly complete, with C, P1-4, and 

 Mi-e. Fig'd, Marsh 1887, PI. X, fig. 3; Lull 1917, PL XVI. 



Horizon and LocALiTV.^Morrison formation, Quarry 9, Como Bluff, Wyoming. 



Diagnosis.— Cheek teeth P4 Mg. M7 slightly larger than M7 of D. striatus. M1-2 

 slightly smaller than M1-2 of D. crassus or D. affinis. Mandible somewhat longer and 

 deeper than in the other supposed species. 



Dentition 



The incisors are not known, but from alveoli they numbered at least three and 

 possibly four, and they were arranged in an anteroposterior series as in the dryolestids. 



The canine is a large tooth, higher than any which follow, and implanted by two 

 separate roots, the anterior a little smaller and more nearly vertical. The tip is re- 

 curved, pointing backward and inward, the anterior margin convex, the posterior con- 

 cave in lateral profile. There is a small heel. The tooth is not unlike that of Laolestes. 



The four premolars are similar save in size and some minute details. Each has a 

 single trenchant, somewhat elongate main cusp, its sharp point directed slightly back- 

 ward and also inward. On the posterior slope of this cusp is an accessory cusp, less 

 strongly marked on the anterior than on the posterior premolars. In the type of this 

 species it is worn off on Pi. There is also a smaller anterior accessory cusp, somewhat 

 higher on the crown, and also less marked on the more anterior teeth. Each premolar 

 has a prominent, sharp, continuous internal cingulum. This runs around the posterior 

 end of the tooth, forming a small posterior heel or cingulum cusp or, as on P4 of the 

 type, two distinct small cusps, one posterointernal and one posteroexternal. On P3-4, at 

 least, the cingulum passes onto the external face and then forward and upward, becom- 

 ing obsolete before reaching the middle of the crown. On P4 the cingulum may also 

 run around the anterior end of the tooth, forming a small anteroexternal cusp, and 

 onto the external face. The external cingulum is always interrupted in the middle, 

 however. 



P2, contrary to the almost universal rule, is smaller than Pi. It is apparently in 

 process of reduction and does not appear until the other premolars are already in place. 

 P3 and P4 in this species are of almost the same size, although P3 may be a trifle shorter 

 and more slender. Both are larger than Pi. 



Each molar has seven distinct cusps, each with its own size, shape, and invariable 

 relationships to the other cusps. M5-6 are the largest and most typical and they may be 

 described first. The contour, as seen from above, is not triangular as in other panto- 

 theres but rectangular, about one and one-half times as long as broad, with rounded 

 corners. The outer face is convex, save for a shallow vertical median groove, and rises 

 to a high, slightly recurved external cusp, slightly anterior to the midline. This is the 

 largest cusp on the tooth and is undoubtedly the protoconid. About halfway up its 



