23 



Family IV. THALLASSITES * Dumeril ct Bibron. 



CHARACTERS. 



1. The shell is depressed and sub-cordiform. 



2. The head is large and sub-quadrilateral, in some (Chelonia) covered with 



plates; in others (Sphargis) with a coriaceous skin. 



3. The neck is short, thick, and not retractile. 



4. The extremities are of unequal extent, the anterior having twice the length of 



the posterior. Both are greatly elongated, and so depressed or flattened, 

 that the bones of the hands and feet, although formed of separate pieces, 

 are incapable of distinct motion upon each other, but make a strong fin, 

 useful only in swimming. Two genera are included in this family, Chelonia 

 and Sphargis. 



* eA\a<r(no!, e«\aTT(oj, in marl frequens. 



V. 2—3* 



