CHAPTER II 

 CLASSIFICATION 



THE Mollusca are divisible into five principal 

 groups or classes : 



Class I. : The AMPHINEURA, of which the 

 Chitons (Coat-of-Mail Shells) are the type. 



In these the body is more or less elongate, without 

 a distinct head, the foot forming the ventral surface. 

 The extremities of the alimentary canal lie at either 

 end of the body, and do not in any way approximate 

 each other, while the various organs are situate in 

 pairs on either side of the central axis, so that the 

 two halves of the body correspond, and the animal 

 is symmetrical. 



This Class is divided into two orders, Polypla- 

 cophora and Aplacophora. 



Order I. : Polyplacophora, the Coat-of-Mail 

 Shells, or Chitons (Plate IX., Figs. 1-3 ; Radula 

 Plate III., Fig. 11) are readily distinguished by 

 being alone amongst the Mollusca in possessing a 

 shelly covering of many pieces, called the " lorica." 



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