1903] Lower Jaw OF Dryptosaurus incrassatus. 137 



species of Trachodon* (and possibly also of the genera Monoclonius 

 and Tnceratops and their allies), in which the teeth move upward 

 in well defined grooves in the inner surface of the outer wall of 

 the dental chamber, whilst the surface of the inner wall of the 

 chamber is comparatively even and smooth. The partitions be- 

 tween the alveoli in Dryptosaurus seem to form part of, and to be 

 continuations or extensions of, the inner surface of the outer den- 

 tary wall inward toward the dentary plate with which they are 

 apparently not connected. In the left ramus of the specimen 

 shewn in figure i, the crowns of all the teeth except the twelfth 

 are broken off close to the alveolar border leaving sections of their 

 bases exposed at this level, so that the exact position of the teeth 

 is definitely determined. In the right ramus of the same speci- 

 men, however, seven of the teeth (seen only in the right aspect of 

 the specimen) are preserved intact. In the specimen figured in 

 plate II fourteen teeth of the left ramus are preserved, whilst in 

 advance of the anterior full-sized tooth a small tooth partially 

 protudes at a lower level. This tooth is apparently an additional 

 one in the series and not a successional tooth, making the total 

 number, in the complete dental series, fifteen. It is truncated 

 posteriorly so as to be similar in shape to some of the teeth 

 described by Leidy, under the name Deinodon horridus** as being 

 peculiar in form, and to a tooth referred to by the writer in his 

 description of Orniihomimus alfus*** as being from the anterior 

 portion of the jaw. No successional teeth have been observed in 

 either of the specimens of Dryptosaurus horn the Edmonton series. 

 The teeth of this species (without reference to such as may be 

 considered to be incisors) are carinated on their anterior and 

 posterior edges, the carinations being minutely serrated, with 

 about ten to twelve denticulations in a space of 5 mm. They are 

 lenticular in section above (figure 7), but in passing downward a 



* Contributions to Canadian Palaeontology, vol. Ill (Quarto), part II, 

 " On Vertebrata of the Mid-Cretaceous of the North West Territory," by 

 Henry Fairfield Osborn and Lawrence M. Lambe, pp. 73 and 78. 1902. 



** Trans. Amer. Philos. Soc. Extinct V^ertebrata from the Judith River 

 and Great Lig^nite Formations of Nebraska, by Joseph Leidy. i860, p. 144, 

 plate 9, figs. 37-40. 



*** Contributions to Canadian Palaeontology. 1902, pp. 53, pi. XIV. 



