INTRODUCTION. 13^ 



CHAPTER III. 



CLASSIFICATION OF SHELLS. 



LINN^US ranks Testacea as the third order in liis sixth 

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

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

 Univalves. 



I. MULTI VALVES. 



SHELLS WITH MANY VALVES. 



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. 



SHELLS WITH 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. 



