473 



LETTER XXV. 



THE CONCIIOLOGIST's NOMENCLATUKE. THE CEPHALOUS 



MOLLUSCA. 



The shells of the Cephalous Mollusca are either, 1, multi- 

 valve ; 2, simply univalve ; 3, spiral or turbinate ; or 4, mul- 

 tilocular or chambered. 



r. MULTIVALVES = MULTIVALVIA, LIN. 



A multivalve shell (Fig. 91) consists of eight pieces (scuta) 

 arranged in a series along and across the back of the animal 

 it covers (Fig. 91).* It is peculiar to a single family or sec- 

 tion of Gasteropods. 



Fig. 91. 



2 



■^•. 



-^K 



The valves are connected together by the mantle forming 

 a marginal hand or zone, which surrounds the whole shell. 

 (Fig. 91, ^.) 



The valves are imbricate when they touch each other along 

 the transverse margin ; and separate when they lie remote 



* " Testae phues, longitudinaliter digestse, dorso incunibeiites." — Lin- 

 naeus. 



