CLASS III]. GASTEROPODA. ORDER II. CYCLOBRANCHIATA. 9 
ticed, still upholds that there is a close affinity between the Chitones 
and the Lepades, considering them as intermediate in their organization 
between the Mollusca and the Crustacea; their affinities have, however, 
been deliberately analysed by Deshayes in his new edition of Lamarck ; 
the anatomical relations of both are carefully set forth, and leave little 
doubt of the fallacy of this arrangement. 
The genus Chiton is one of peculiar interest, because it is the only 
instance of a mollusk having a multivalve shell; but if the shell be com- 
pared with that of Patella, their analogy is not so remote as to prevent 
the expectation of a certain resemblance in their animal inhabitants ; 
the shell of the former offers the same convex surface as that of the lat- 
ter, and differs only in being divided into eight pieces. The animals of 
both have the same ventral disc by which they acquire motion; the 
nature and position of their branchiz are the same, and they have the 
same distribution of vessels; the mantle, however, of Chiton is distin- 
guished by its hard, fibrous, cartilaginous composition, necessary to sus- 
tain the multivalve construction of the shell. 
In one species, the Chiton amiculatus (Plates CXXXII. and CXXXIII. 
Fig. 80.), the mantle is expanded entirely over the shell, and it has on 
this account been separated by Gray for the formation of a new genus, 
Amicula ; this unusual expansion of the mantle, however, is but a pecu- 
liar modification of that organ ; the valves of the shell are set in the same 
order and position as in the rest of the Chitons. 
The shell of Chiton may be described as being oval, regular, and com- 
posed of eight pieces or valves ; the valves are transverse, convex, and 
somewhat beaked in the middle; the surface is either smooth, imbri- 
cated, or variously striated, and they are set in a regular series; the 
dorsal edges of the valves lean one upon the other, moving like plate- 
armour, and the sides are firmly set in the cartilaginous cuticle of the 
mantle, which is either smooth or coriaceous, or covered with spines or 
hair. 
The Chitones are very abundant, and may be found at low water upon 
stones or fragments of rocks, to which they adhere with great power of 
suction. They have been vulgarly called the Sea Wood-lice, because, 
VOL. II. (o} 
