198 PROCEEDINGS OF THE ACADEMY OF 



inches lonf^. The broken end is 8 lines wide and 1| lines thick ; the widest 

 and thickest part of the mould near the middle of the length of the tooth is 

 Hi lines wide and 5 lines thick. 



The fangs of the teeth do not continue of the same width to the bottom, as 

 in the teeth of crocodiles, and, as I believe, is considered to be the case in 

 Megalosaurus^ but from about their middle they contract, or become narrower, 

 as is ordinarily the case in mammals. Indeed, one of these teeth isolated 

 might be taken for the canine of a Drepanodon, or sabre-toothed tiger. In 

 the fossil the bottoms of the fangs narrow antero-posteriorly, and become 

 thinner from without inwardly, and they also curve somewhat in the latter 

 direction. 



The long fangs of the teeth in the fossil, and their becoming narrowed at 

 bottom, at first led me to suspect the specimen belonged to a different genus 

 from ilegalosaurus, but a view of fig. 1, plate xii, of Prof. Owen's raonograjih 

 above mentioned, seems to prove by the appearance of the successional teeth 

 within the jaw, that the fangs actually become narrowed towards the bottom 

 in that genus. 



In the best preserved tooth of the fossil, the enamelled crown exhibits the 

 same shape, familiar as the characteristic form of \.\\&i of Mcgalosaurus. The 

 trenchant borders of the crown are denticulate, and the enamel is compara- 

 tively smooth, or only very feebly striate. 



The contracted condition of the bottom of the fangs of the teeth would 

 leave more space than there otherwise would be for the derelopment of suc- 

 cessional teeth within the jaw. In the fossil the remains of one of the latter 

 is seen at the lower part internally of one of the functional teeth, and an im- 

 pression in a corresponding position of the other functional tooth indicates 

 a similar occupant. 



In the progress of the successional teeth of 3Icgalosaurus, their summit 

 first appeared at the margin of the jaw internally to the teeth in functional 

 position. In the course of growth and protrusion they excited absorption in 

 the contiguous bone and fang of their predecessors, and continuing to ad- 

 vance from within and beneath (in the lower jaw), as it were, shouldered the 

 latter from the jaw. A third tooth in Megalosaurus appears to have occupied 

 a position internal to the second one, before the protrusion of this from the 

 jaw. 



The outer portion of the jaw bone retained in the specimen has an average 

 depth from the alveolar border of 5 inches. Its outer surface is a vertical 

 plane, rounding only near the base. 



The present opportunity is an appropriate one to make a few remarks on the 

 American 2i\\\Q?, of Megalosaurus. Since I have had the opportunity of inspecting 

 theremains of the remarkable reptile from the green sand of New Jersey, de- 

 scribed by Prof. Cope (Proc. 1866, 275) under the name of Lxlaps Qqicilunguis, in 

 observing the comparative uniformity of the teeth, identical in character with 

 those of Megalosaurus, I am more strongly impressed with the idea that the 

 teeth of like shape forming part of those referred by me to Dinodon, alone 

 belong to this genus. The others, of which no representatives have been ' 

 discovered or recognized as belonging to Megalosaurus or Lcelaps, most pio- 

 bably indicate a distinct genus and species, for which I propose the name of 



ACBLYSODON MIRANDUS. 



Future discovery may prove Lxlnps and Dinodon identical, and, judging 

 from the comparison of corresponding parts of the jaws and the teeth, will 

 be found to be more closely allied to 3Iegalosaurus than was suspected, even 

 should they not prove to be generically the same. 



It is clear, from an examination of the anterior portion of the mandible of 

 MegalosaMrus described and figured by Buckland, Cuvier, Owen, etc., that no 

 such teeth as those now referred to Aublgsodon occupied the forepart of the 

 jaw. It is also probable that the upper teeth of Megalosaurus and of its 



[August, 



