23 



Family IV. THALLASSITES.* Dumeril et 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 (Spargis) 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 

 Spargis. 



* eaAis-cricc, fio>.iiTT;6t, ill mari frequens. 



