AET. 16 



FOSSIL EEPTILES FROM MONTANA GILMORE 



35 



upper as would be expected. Both surfaces of the crown are marked 

 by fine, irregular, vertical wrinkling. The line of smaller denticles 

 on the anterior border curve inward while those of the posterior 

 border curve outward, so that viewed from the end, the line of 

 denticles form a sigmoid curve. The roots of the teeth are long, 

 smooth surfaced, and subcylindrical. 



These teeth have the general characteristics of other North Ameri- 

 can armored Dinosauria; that is, laterally compressed crowns with 

 denticulated borders, basal cingulum, and long more or less cylindri- 

 cal roots. Teeth are now known of the following genera : Stegosaurus, 

 Ankylosaurus^ Stegopelta, Princonodon^ Palaeoscincus^ Panoplosau- 

 rus, Ed?nontoma, and Dyoplosaurus. Compared with teeth of these 

 various genera those belonging to the present specimen have their 

 nearest resemblances in ^ ^ c 



those of Dyoplosaurus. 



Through the kindness 

 of Dr. W. A. Parks, a 

 maxillary fragment con- 

 taining teeth of the type 

 of Dyoplosaurus acuto- 

 squatneus was loaned me 

 for study. A direct com- 

 parison of these teeth 

 with those of the specimen from the Two Medicine formation shows 

 such close similarities in size, proportion, denticulation, and sculpture 

 as to leave no doubt that the two specimens are cospecific. This max- 

 illary fragment of the type was regarded by Parks ^^ " as the anterior 

 portion of the dentigerous region of the left maxillary," but, after 

 comparing it with the broken maxillae of the skull here considered, I 

 am fully convinced that it represents the posterior portion of the right 

 maxillary. This determination is of importance as definitely fixing 

 the position of the teeth in the jaws; that is, the highest j)art of the 

 crowns are toward the posterior border. It was also found that the 

 published illustration of the tooth does not accurately depict the 

 original, being in error in that the denticles on the anterior border 

 are too acutely pointed and too widely spaced. The second denticle 

 posterior to the apical one should be lower, and the first point pos- 

 terior to the apical denticle should be omitted, a fact recognized by 

 Doctor Parks; on the posterior border at least two denticles should 

 be added. These are now plainly shown on the specimen, though 

 previously hidden by adhering matrix. In the Canadian tooth, how- 

 ever, they are barely visible from a lateral view, passing more to 



Figure 18. — Right maxillary tooth of Dyoplo- 

 saurus ACUTOSQUAMEUS PARKS. NO. 11893, 



U.S.N.M A, Inker view; B, Outer view; G, 

 Posterior view. All three times natural size 



Univ. Toronto Studies, No. 18, 1924, p. 9. 



