INTRODUCTION. 13 



CHAPTER III. 



CLASSIFICATION OF SHELLS. 



LINNiEUS ranks Tcstacea as the third order in his sixth 

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

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

 Univalves. 



I. MULTIVALVES. 



SHELLS W^ITH MANY VALVES. 



1. Chiton: Valves placed in transverse plaits down the 



back, 



2. Lepas: Valves unequal ; body sessile. 



S. Pholas. Shell bivalve, with accessory valves at the 

 hinge. 



11. BIVALVES. 

 shells m'ith two valves. — conchs. 



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. 



