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IX. On the Structure of Chitons. By J. E, Gray, Esq., F.R.S., F.Z.S., 8fc. 
Received June 17, — Read June 17, 1847. 
LiNN^US and most of his successors arranged the Chitons with the Pholades and 
the Balani, as multivalve shells. Adanson, with his usual tact, placed them with the 
Patellce, and the anatomy of the animal, published by Poli and Cuvier, has shown 
the propriety of this position. M. de Blainville separated the Chitons from the 
other Mollusca, with whieh they had always been placed on aecount of tbeir possess- 
ing a series of imbricated shelly valves arranged along the central line of their back, 
and placed them with the Cirripedes in a peculiar subclass, which he called Articu- 
lated Mollusea, and considered as intermediate between the two divisions of the 
animal kingdom. I need scarcely observe that this division has not been adopted, 
the Cirripedes having now been proved to be true Crustacea. 
There are a few peculiarities in the internal structure of these animals not found 
in other Mollusea. The shells also offer some differences, which have not, as far as 
I am aware, been previously noticed, and which it is the object of this paper to 
describe. 
The Chitons at first sight differ from all the other Mol- 
lusca in being provided with a series of imbricated valves, 
forming a line down the centre of the back, and in this 
character they differ essentially from the Patellce, to whieh 
they are most nearly allied in the general form, the posi- 
tion of the gills, &c. I have therefore thought it desirable 
to examine these valves with reference to one another, and 
to determine whieh most resemble the valves usually found 
on other Mollusea, and which are the additional or supple- 
mentary valves. 
The posterior terminal valve (fig. 1 , C and F, fig. 2, C) of 
the more normal Chitons, as in the restricted genus Chiton 
for example, most nearly resembles the conieal form which 
the valves of Mollusca generally assume, and the other 
valves are only modifieations of the same form. 
The seven anterior valves are formed like the posterior 
one, but with the greater part of the hinder half deficient, 
and with the front edge of insertion somewhat enlarged. 
In the front valve (figs. 1 and 2, A and D) the anterior 
Chiton striatus. 
