308 



our observation among the numerous monuments of the 

 natural history of the ancient world. 



The only fossil remains by which the presence of any 

 saurian reptile could be determined in the Montmartre 

 quarries, was a frontal bone of a crocodile of a small size. 



Tortoise. — The carapace^ or buckler of these animals, 

 is formed by the eight pair of ribs and the annular portions 

 of the nine dorsal vertebrae, which spread so as to unite, 

 by suture, into one piece. The plastron, or breast-plate, is 

 a second buckler formed by the sternum, which in tortoises 

 is composed, according to M. Geoffroy, of nine bones, 

 commencing at nine points of ossification, but not always 

 meeting so as to form a continuous surface. 



The sea-tortoise (chelone^ Brongniart), which agrees with 

 the soft tortoise {trionyx, Geoffroy), as respects its breast- 

 plate, resembles the common tortoise in another point ; the 

 whole circumference of the carapace is girt with bony pieces 

 united to each other and to the ribs. These encircling 

 pieces, which M. Geoffroy compares to the cartilaginous 

 parts of ribs, are wanting in the soft tortoises, or, at least, 

 always remain cartilaginous or membranous, so that the 

 middle part only of the carapace is supported by a bony disk. 



To distinguish the genus to which any of these coverings 

 may belong, it is only necessary, as Cuvier teaches, to com- 

 bine, with the foregoing characters, such as are yielded by 

 their forms. These are, in the land-tortoise, always oval, 

 vaulted and pointed forwards ; in the sea-tortoise, elliptical 

 and tumid ; and more or less depressed in the fresh-water 

 tortoise; with a rough and shagreened surface in the soft 

 tortoises ; and raised in different projections in the chelydes 

 and the serpentine. 



The feet also furnish distinguishing characters of the 

 subgenera of these animals : thus, they are very long, with 

 very unequal toes in the sea- tortoise; the toes are exceed- 



