ON THE PERMIAN CHITONID.E. 251 



apophyses at each extremity, which are united to the processes 

 bounding the posterior margin at the junction of that margin 

 with the anterior ; the process of insertion of the posterior margin 

 is somewhat produced, and follows the contour of the exposed 

 edge. 



Three intermediate plates of this species have been found, all 

 of which strongly resemble each other. One of them is slightly 

 longer compared with its width than the others; and there also 

 exists a little variation in the mesial angularity of the plates. 

 In no other respects do they differ. Owing to the hard matrix 

 in which these plates are imbedded, it has not been possible to 

 work out their processes of insertion. In consequence of this, 

 some uncertainty exists of their true specific affinity with the 

 postal plate which has been described with them. The latter 

 plate is assumed to belong to the same species as they, as it 

 possesses a similar angularity of form, and as there is nothing in 

 its general character incompatible with specific identity with 

 them. But, when a plurality of species of ChitonidcB occur in 

 so fragmentary a condition as the Permian species, it is sometimes 

 an impossibility to speak with certainty on the true correlation 

 of plates; so that the present assumption must be cautiously 

 received, and looked upon more as a suggestion than anything 

 stronger. 



The anterior process of insertion of the posterior plate is very 

 peculiar, and appears to differ from that of any other species. 

 In the generality of species, if not in all, the plates are inserted 

 or attached to the mantle by a mere marginal development of 

 the substance of the plate, or by an imbedding of a portion of 

 the plate itself; but in this case there is added to the usual 

 process a lamella, which, with the margin of the plate, forms a 

 very complex mode of attachment to the mantle. The value of 

 this feature is a point yet to be determined; and though I only 

 attach to it specific importance at present, I am rather disposed 

 to believe that further investigations will assign it greater value. 



The intermediate plates of this species bear a close resemblance 

 to those of the recent species C. hastatus, particularly to those 

 posteriorly placed. The second plate of C. scutiger is also 



