FOSSIL TESTUDINATA. 255 
mi nation of the secondary formations ; when the 
Ichthyosauri and Plesiosauri became extinct, 
and forms of Crocodiles, approaching to the 
Cayman and the Alligator, were for the first 
time introduced. 
SECTION XII. 
FOSSIL TORTOISES, OR TESTUDINATA. 
Among the existing animal population of the 
warmer regions of the earth, there is an exten- 
sive order of reptiles, comprehended by Cuvier 
under the name of Chelonians, or Tortoises. 
These are subdivided into four distinct families ; 
one inhabiting salt water, two others fresh water 
lakes and rivers, and a fourth living entirely 
upon the land. One of the most striking cha- 
racters of this Order consists in the provision 
that is made for the defence of creatures, whose 
movements are usually slow and torpid, by in- 
closing the body within a double shield or cui- 
rass, formed by the expansion of the vertebrae, 
ribs and sternum, into a broad bony case. 
The small European Tortoise, Testudo Graeca, 
and the eatable Turtle, Chelonia Mydas, are 
familiar examples of this peculiar arrangement 
both in terrestrial and aquatic reptiles ; in each 
