INTRODUCTION. 21 



CHAPTER III. 



CLASSIFICATION OF SHELLS. 



LINNiEUS ranks Testacea as the third order m his sixth 

 class of animals called Worms. He has made three prin- 

 cipal or grand divisions, viz. Multivalves, Bivalves, and 

 Univalves. 



I. MULTIVALVES. 



SHELLS WITH MANY VALVES. 



1. Chiton: Valves placed in transverse plaits down the 



back. 



2. Lepas: Valves unequal; body sessile, or on pedmicles. 



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



hinge. 



II. BIVALVES. 



shells with two valves. 



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



let into the opposite valve. 



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. 



