Shell Life 



triangular areas, known as the median and lateral 

 areas. The first and last plates are not so divided, 

 and are generally sculptured in harmony with the 

 lateral areas of the intermediate plates. Turned over 

 on its back the Chiton will be seen to have a close 

 likeness to the underparts of a Limpet. But closer 

 inspection will show that though it has a head there 

 are no tentacles and no eyes. The respiratory organs, 

 too, diflfer from those of the Limpet. These matters 

 we have already dealt with in the early chapters. As 

 the shell-plates are perforated by 

 numerous pores whose mouths 

 are occupied by sense organs, it 

 is probable that the animal can 

 get on as well without eyes as 

 the Limpet can with them. The 

 Mail-shells are provided with a 

 radula of much more advanced 

 type than that described in the 

 Tusk-shells. In tliat of Chiton 

 there are 17 teeth in each row. 

 There are ten or twelve native species of Chiton ; 

 the large figure on the previous page is not British 

 but a well-known West Indian species {G. squartiosiis), 

 selected as a type on account of its superior size. 

 The British forms are : — 



The Bristly Mail-shell (C. fascicularis), whose dis- 

 tinctive feature is the spiny girdle and the series of 

 tufts of bristles along either side of the shell-plates. 

 The latter are shield-shaped with a central keel, and 

 equal to three-fifths of the entire breadth of the animal. 

 The colour varies a good deal from yellow and orange 

 to pink, red, or deep brown, marked with lines and 



Underside of Chiton, and 

 a, profile of head 



