CHAPTER II 
CLASSIFICATION 
HE Mollusca are divisible into five principal 
groups or classes: 
Crass 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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