X34 



The Ottawa Naturalist. [November 



The skull discovered in 1884, figure i, is somewhat larger 

 than the one found in 1889, figure 2. In both, the right ramus 

 of the mandible is displaced downward so as to reveal its inner 

 surface. In the 1884 specimen both halves of the mandible are 

 preserved almost in their entirety. The left ramus lies against the 

 lower left half of the cranium so as to conceal its inner surface 

 in the vicinity of the anterior half of the surangular, and the cor- 

 responding part of the right ramus is hidden by some of the bones 

 of the palate. In both rami, unfortunately, a considerable part 

 of the lower border is missing below the front part of the sur- 

 angular. The 1889 specimen consists of the anterior parts c f the 

 skull, the lower jaw lying against the palate so that the inner 

 surface of the left ramus and the outer side of the right one is 

 hidden. The left ramus is preserved for about three-fourths of its 

 entire length from the front but the right ramus is broken off at 

 about its mid-length. 



In comparing the mandible of Dryptosaurus incrassatus with 

 that of the Jurassic Ceratosaurus nasicornis of Marsh, it is seen, 

 that theiormer is deeper, in proportion to its length, than the latter, 

 otherwise the general contour in both species is somewhat similar. 

 In the Canadian specimens the following elements of the 

 lower jaw are more or less clearly exhibited :— the dentary, the 

 surangular, the angular, the articular and the splenial, with a 

 presplenial. The coronoid is in both specimens either not pre- 

 served or is covered by other bones of the skull. 



The dentary is a large and robust bone extending backward 

 to beneath the articular cotylus. Its greatest depth is attained 

 at about its mid-length, where it meets the surangular and narrow- 

 ing rapidly passes backward below that element, overlapping it 

 posteriorly as a thin plate terminating in an acute point, figure 3. 

 On the inner surface the dentary occupies about one-half of the 

 lower depth of the jaw anteriorly, narrowing backward gradually 

 until it passes to the outer surface. In the amount of its back- 

 ward extension it equals that of the dentary of Sphenodon as 

 described by Giinther in the Philosophical Transactions of the 



Royal Society of London in 1868.* ^___ 



* " Contribution to the Anatomy of Hatteria (Rhynchocephalus, Owen).' 

 Philos. Trans. Royal Soc, vol. 157, p. 595, pi- xxvi, fig. 7. 



