CLASSIFICATION. 



LINNAEUS has made three principal or grand divisions 

 of Testacea, viz. Multivalves, Bivalves, and Univalves; of 

 which he has given the following generic description. 



I. MULTIVALVES. 



1 . Chiton : Valves placed in transverse plaits down the back. 



2. Lepas: Valves unequal ; body sessile. 



3. Pholas : Shell bivalve, with accessory valves at the hinge. 



II. BIVALVES. 



/ 4. Mya : Hinge with generally a broad thick tooth, not let 



into the opposite valve. 

 o 5. Solen: Shell open at each end; hinge with a single or 



double subulate reflected tooth, not let into the opposite 



valve. 

 ^ 6. Tellina: Hinge with the lateral teeth of one valve not 



let into the other. 

 y^ . 7. Cardixjm: Hinge with remote penetrating lateral teeth. 

 ^ 8. Mactra: Hinge with a complicated triangular middle 



tooth, and an adjoining hollow. 



