Remains in Magnesian Conglomerate. 353. 



as in other animals,, but would present a succession of narrow and deep de- 

 pressions corresponding- to the body of each vertebra (Pigs. 6. and 7.). The 

 inferior surface in the vertebra (Fig. 6.) presents a concavity to the depth of 

 -rV^^hs of an inch. 



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

 each vertebra, be one-half more than at either of its points of junction with 

 the next vertebrae. Traces of the same peculiarity are visible in two other 

 specimens. 



The leading characters of these vertebrae are, 1st, their double concave 

 system; 2nd, the hour-glass form of the annular portion ; 3rd, the sutures con- 

 necting the bodies with their processes; and 4th, the peculiar form of the 

 vertebral canal. 



With regard to the first character, it separates our animal remains from all known recent ge- 

 nera ; while the third character separates it from the recent Saurians excepting the Crocodile. 



Although the concavo-convex system pervades nearly all the recent Crocodiles and Lizards, it 

 by no means applies with regard to the determination of their extinct genera. Thus the Croco- 

 diles of Honfleur, of Caen, of Tilgate, have a slight concavity of the articulating surface of each 

 body. The Megalosaurus has the same peculiarity. The whole of the Enaliosaurians are more 

 or less doubly concave; in fact, nearly all the more ancient extinct Saurians are thus charac- 

 terized. 



We know of no other remains having such deep concavities as those in question, except the 

 Ichthyosaurus ; but our specimens evidently do not belong to that genus from their other pro- 

 portions, which separate them in the most distinct manner. 



Thus their antero-posterior diameter is double in proportion to that of the Ichthyosaurus. 



The hour-glass form of the bodies, the deep concavities, and the sutures, would likewise ex- 

 clude them from the Monitors. 



These characters bring them nearer to the Crocodiles of Honfleur and the Megalosaurus, than 

 to any other remains with which we are acquainted ; and with regard to the latter, the difference 

 in size is certainly a great objection ; but this circumstance is not sufficient to invalidate our 

 opinion, since there are instances of as great differences where analogies as close have existed. 



The peculiar form of the canals of some of our specimens of vertebras, is so novel to us, that 

 we shall not at present attempt to found any conclusion upon it, but await the chance of future 

 opportunities of studying its nature. 



Chevron Bone. — Plate XXIV., fig. 9, natural size. This bone, which is 

 very nearly perfect, we consider to be a chevron bone. 



/?i6s.— Plate XXIX., fig. 10, natural size. 



We have ribs of two types, — one flat, the other round. We have not as- 

 certained the forms of either of the extremities of the flat ribs. Fig. 10. is a 

 rounded rib, and has a double head, with a deep intercostal groove. 



