30 MOLLUSCA— CLASS I TROPIOPODA. 



MOLLUSCA CONCHIFERA*. 



Animalia tnollia, inarticulata, pallio auiplo instructa, per branchias re- 

 spirantia, testa calcarea a fluido mucoso gradatim perfecta, partim 

 vel totaliter tecta. 



The Conchiferous Mollusca constitute a vast series of animals exhibit- 

 ing the highest degree of organization of those which are without skele- 

 ton or vertebrae. They are characterized as being furnished with a large 

 fleshy mantle, and are either wholly or partially covered with a calca- 

 reous shell, which is gradually formed by the secretion of a mucous 

 fluid, which becomes hardened on the body. 



The organ of locomotion, which is selected to characterize the primary 

 distribution of the Mollusca, serves to divide them into five classes as 

 follows, under each of which their general physiology will be detailed 



TROPIOPODA. 



BRACHIOPODA. 



GASTEROPODA. 



PTEROPODA. 



CEPHALOPODA. 



Class I. TROPIOPODA. 



Animal in testa bivalvi perpetuo affixum, capite oculisque nullis ; ore 

 nudo, abscondito, partibus solidis nullis ; pallio amplo corpus to- 



* It is obvious that this word is used to distinguish the shell-bearing from the nuked Mol- 

 lusca. Lamarck applies the term - Conchifera" to the bivalve Mollusca only; in fact, its 

 derivative is so rendered by some authors ; it however frequently occurs in the ancient poets 

 in reference to the Trumpet Shell (Triton tuba) and other univalves. 



