Description of a Fossil Chiton from the Silurian Rocks, with remarks on the fossil species of the genus

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Abstract
The discovery of a species of Chiton in beds of undoubted Silurian age appears to be a fact sufficiently important to be brought under the notice of the Geological Society, not only from the rarity of the genus in a fossil state, but because it carries back to an earlier date another of the many families we are in the habit of considering as characteristic of later epochs. The shell I have now to describe presents peculiarities distinguishing it both from recent species, and also from those found in the carboniferous rocks. In introducing the subject I propose to glance at the ordinary characters of the family, for so this group must be considered, in order to show the relation of the fossil with the living species. The Chiton is one of the lowest forms of Gasteropodous Mollusca, and is considered by naturalists as closely allied to the genera Patella and Lottia , and as forming with them a distinct order of Mollusca under the name of Cyclobranchia (Cuvier), distinguished by the arrangement of the branchiæ. The Chitons have a double generative system, terminating (according to Blainville and Rang) on either side of the body. This is a very marked character, and one indicating strongly the the low position the group holds in the order to which it belongs. The shell is of course the only part with which we have to do (in treating of fossil species), and its variations are fortunately accompanied by differences in the structures of the

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