136 The Ottawa Naturalist. | November 



anteriorly the ang^ular increases considerably in depth reaching- 

 the coronoid above and the splenial in front. 



The broad lamellar bone immediately above the dentary on 

 the inner surface of the ramus (figure 2) is the splenial. It is mis- 

 placed in the specimen figured in plate I, and it is seen in section 

 in its proper position in both skulls at the points e and /in figures 

 I and 2 respectively. It is perforated near its anterior end and 

 close to its lower border by a large oval foramen. At a short 

 distance behind this foramen a well marked emargination of the 

 bone occurs, visible in both specimens but shewing more decidedly 

 and to a greater extent in the skull figured in plate I. The outline 

 of this emargination bears a strong resemblance to the anterior 

 end of a second foramina! opening, which if it did exist, may have 

 been partly formed by the angular as in Crocodilus. 



Continuing forward trom the splenial is a narrow presplenial 

 that apparently reaches to, or almost to, the front limit of the 

 dentary. 



Above the presplenial the inner alveolar plate of the dentary, 

 of about the same depth as the presplenial, forms the inner wall 

 of the dental chamber and completes the inner anterior surface of 

 the ramus. It meets the splenial posteriorly and narrows rapidly 

 upward, but its relation to the dentary and the splenial, behind 

 the dental series, has not been ascertained. Its upper border is 

 at a lower level than the outer alveolar border of the dentary. 



In Megalosaurus the l)ony partitions dividing the alveoli from 

 each other are described* as springing from the inner alveolar 

 wall and projecting outward to the inner surface of the outer wall. 

 The reverse of this seems to be the case in Dryptosaurus, in which 

 the principal alveolar grooves are apparently formed on the inner 

 surface of the outer dentary wall with little or no development of 

 grooves in the alveolar plate. In this particular the alveoli of 

 Dryptosaurus are somewhat similar in general plan of structure to 

 those of the dental chamber of the mandible of the Cretaceous 



* "Notice on the Megaiosaurus or great Fossil Lizard of Stonesfield," 

 by the Rev. William Buckland. Trans. Geol. See, London, second series, 

 vol. I, p. 395, pis. XL and XLI, 1824 ; and "On the Skull of Megalosaurus," 

 by Professor Owen. Quart. Jour. Geol. See, London, vol. XXXIX, p. 339, 

 pi. XI, 1883. 



