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LETTER XXV. 



THE CONCHOLOGIST'S NOMENCLATURE. 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. 



I. 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. 



The valves are connected together by the mantle forming 

 a marginal land 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 



* " Testse plures, longitudinaliter digestae, dorso incumbentes." LJN- 

 NJEUS. 



