ON THE PERMIAN CHITONID^. 247 



perfect series without it. Neither does there appear to be any 

 reason for assuming the width of this Chiton to have been less 

 towards one extremity than the other ; for when a perfect series 

 of plates, which by their lines of increment appear to be of one 

 age or state of growth, is obtained, no such difference is observed. 

 The central plates are always rather wider than those near the 

 extremities ; but the difference is not great, and is of about the 

 same degree at each extremity. 



From the figures and description of this species given by 

 Prof. King in his " Permian Monograph," he does not appear to 

 have possessed a full series of plates ; but, respecting their 

 arrangement, he seems to have somewhat similar views to my 

 own. 



As previously mentioned, this Chiton resembles many recent 

 species. It does not appear that any of the palaeozoic species 

 have a very strong similitude to it. Prof. De Koninck, in 

 describing an Upper Silurian species (C. Wrightiatius), states that 

 it has some resemblance to the present ; * but, from his figures of 

 the two plates discovered, I should imagine that its resemblance 

 is greater to C. cordatus, which appears to belong to the same 

 type. In the close juxtaposition of its plates it is like the next 

 species (C. Hoivseanus)] but it differs from it in the greater width 

 of its plates, and in several other particulars, which will be 

 noticed in the remarks on that species. In the short and trans- 

 verse form of its intermediate plates it somewhat resembles the 

 Chiton Scaldianus of De Ryckholt.f But the palaeozoic species 

 having most resemblance to C. Loftusianus appears to be an un- 

 described form in the collection of Mr. J. H. Burrow, of Settle, 

 from the Carboniferous limestone of that neighbourhood. This 

 Chiton is characterised by the same narrow transverse form of 

 intermediate plate as the Permian species; and its posterior 

 plate, though flatter, is not much unlike that of C. Loftusianus. 



Though the remains of G. Loftusianus are of more frequent oc- 

 currence in the shell-limestone of Tunstall Hill than those of its 

 congeners, it is still a rare fossil there. I have also taken stray 



* Bull, de I'Acad. Roy. de Belg., 2 ser., tome iii., no. 11. 

 t Ibid., tome xii., no. 7, and tome xviv., p. 63. 



