98 SIXTH REPORT — 183G. 



The authors then proceed to some general views : 



" To make our present notice more complete it will be necessary to 

 extract from a former memoir the characters exhibited by a section 

 through the axis of the vertebrae, which exhibit a peculiar form in the 

 spinal canal. In this section we have a mould of the vertebral or spi- 

 nal canal formed by the matrix showing a very peculiar form in the up- 

 jjer portion of the annular element, forming the inferior boundary of 

 the canal. Thus its inferior surface would not be on one level plane 

 like other vertebral canals, but would present a succession of hollows 

 or depressions corresponding to the body of each vertebra, for the in- 

 ferior surface would present a concavity to the depth of -jVth of an inch 

 in our specimen. 



" In this way the vertical diameter of the canal would, at the middle of 

 each vertebra, be at least one third more than at either of its points of 

 junction with the next vertebra : traces of the same peculiarity may 

 be found in other specimens. 



" If we retrace our steps we shall find the pieces lately under review 

 presenting at least two types. 



" To the first belong the caudal vertebrse with the chevrons, and the 

 two others described immediately after them ; that is, a sacral and first 

 caudal ; the two ilia and ischium, the large and small femur, and the pha- 

 langes. 



" To the second the series of caudals without chevrons, and the re- 

 maining bones of the members. 



" The association of the piece of jaw with the latter would be assu- 

 ming more than we could prove ; although its characters are more those 

 of a lizard than a crocodile, yet we cannot show that it belonged to 

 the same animal, for it might have belonged to another extinct sub- 

 genus of lizard. We must recollect that the blocks of stone in which 

 these remains are met with, are sometimes so filled with bones that 

 they would be called osseous breccia by those not aware of their origin. 

 This is a sufficient proof of the multitude of animals whose remains 

 are here enveloped in the magnesian conglomerate, and at the same 

 time a plausible justification of our opinion, that by a careful examina- 

 tion and study of these remains we shall be enabled to make out seve- 

 ral subgenera of Saurians, independently of the remains of fishes. 



" It is singular that in all the vertebrae hitherto met with in this lo- 

 cality we should find the double concave system only. We have al- 

 ready dilated upon the greater resemblance of the vertebrae to the cro- 

 codilian type than to any other ; we have moreover pointed out analo- 

 gies with other parts of their skeleton. 



" Tlie occurrence of crocodiUan remains is both frequent and nu- 

 merous in Great Britain as well as elsewhere : an examination of them 

 according to their geological position, commencing with those at pre- 

 sent in existence on the surface of this earth, and extending to those 

 found in the new red sandstone of Guy's Cliff by Mr. Conybeare, and 

 the instances before us from Durdham Down, will show a regular se- 

 ries of progressive changes in the type of their vertebrae, from the con- 

 cavo-convex of the present day to the same in the newer extinct spe- 



