SYSTEMATIC ARRANGEMENT 



OF 



MOLLUSC A. 



Subkingdom MOLLUSCA. 



Animal soft ; flesh destitute both of a bony skeleton supporting 

 jointed limbs, and of a hard, ringed skin ; covered with a muscular 

 coat called the Mantle endued with a glairy humour, and gene- 

 rally furnished with one or two lateral calcareous envelopes called 

 Shells, which are secreted by this coat for the protection of the body 

 and of the more vital organs of the animal. The body is generally 

 elongate, walking on a single central disk or foot, and provided with 

 one or more pairs of organs on the head and sides. The nervous 

 system (which furnishes the most distinctive character of the larger 

 group of the Animal Kingdom) merely consists of a certain number 

 of medullary masses distributed to different parts of the body, one 

 of the masses being placed over the gullet and surrounding it like a 

 collar. 



Linnaeus refers all the animals inhabiting shells to five genera, 

 viz. Limaoc, Ascidia, Anomia, Clio, and Sejria. These genera may 

 be regarded as the types of the classes proposed by Cuvier. Poli 

 had, before his time, considered three of them as Orders, under the 

 names of Mollusca Reptantia, Subsilientia, and Brachiata. 



Synopsis of Classes. 

 A. Pedifera. Crawling on a foot placed under the body. 



I. Gasteropoda (Gasteropods or Univalves). Head distinct, with 



eyes and tentacles ; body usually protected by a conical, more 

 or less spiral shell, often furnished with an operculum. 



II. Conchifera (Conchifers or Bivalves). Head indistinct; 



mouth placed between the gills ; they and the body enclosed 

 between the two leaves of the mantle, which are covered by two 

 shelly valves united above by a ligament. 



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