THE MOLLUSCA 199 



This arrangement also occurs in the Cephalopoda. Hence 

 these and the gastropods are often classed together, under 

 the title Odontopliora, or tooth-bearers. The most re- 

 markable of the gastropods are the Chitons. These have 

 the shell in eight parts, arranged on the dorsal side in such 

 way that the pointed, posterior edge of each overlaps the 

 one behind. When detached from the rock or stone on 

 which they are found they roll up, armadillolike. 



The species on our shores is Chiton fascicularis. This is 

 about an inch long by five-eighths of an inch wide, of a 

 greyish brown colour, and has tufts of light-coloured 

 bristles along the sides. 



Chiton discrepans (Fig. 87). Somewhat resembling the 

 last, but of larger size, reaching two inches in length by one 

 in breadth. Its colour is mottled greyish brown and 

 white. I believe it is rare on the English coasts, but is 

 very common in the Channel Islands. 



Chiton cancellatus. About three - quarters of an inch 

 long, prettily marbled with grey brown and white, but 

 subject to much variation in colour, often mottled with 

 red and grey. 



Chiton cinereus. About half-an-inch long, slate-grey, 

 but also varied in colour and marking. This is the com- 

 monest species. 



Chiton marginatus, Chiton Icevis, Chiton debilis, are all 

 closely allied. 



Chiton ruber is a beautiful form about three-quarters 

 of an inch long, and of brilliant red. All these are found 

 under loose stones in rock pools. 



Chiton scabridus. This is a species much prized by 

 collectors, as it is supposed to be rare. As a matter of fact 

 it is not rare, but its habitat is a strange one. It lives on 

 the under side of stones which are deeply set in firm, muddy 

 sand, in conditions which do not seem conducive to health 

 or to a decent food supply. It is a small species, about 



