272 NOTES ON THE PERMIAN SYSTEM OF 



and the other three, assuming it liad eight altogether, are ohlong or 

 straj)-shaped in marginal outline. The second, third, and fourth 

 plates are broad and very oblique ; the fifth, sixth, and seventh, nar- 

 row and transverse. The posterior plate, which is not " capuliform^^'' 

 but half-limpet-shaped, has its apex or mucro produced to a fine 

 point. Seen in profile, all the plates, excepting the first or head- 

 plate, are curved towards the posterior margin, considerably ele- 

 vated along the dorsal line, and pressed down steeply on each 

 side towards the lateral margin. The lateral areas of the inter- 

 mediate valves, excepting the second, are large and distinctly 

 defined. Occasionally a small sulcation or furrow may be seen 

 on each side of the dorsal ridge, but this seems to be rather an 

 accidental than a specific character. The entire surface of all the 

 plates is minutely granulated or shagreened, and the stride of 

 growth are very distinct on the dorsal as well as on the lateral 

 areas. The interior of the valves is minutely pitted or granu- 

 lated. The apophyses or processes of attachment of the mantle 

 are large, nearly semicircular, and, as they are confined to the 

 lower half of the dorsal area on each side, they are consequently 

 very widely separated. It, perhaps, may be inferred, from the 

 disparity in the shape and size of the plates, that this Chiton was 

 much narrower in front than behind; and from the greater com- 

 parative length of the anterior plates, it closely approaches some 

 of the recent spinose species, such as C. spinulosus. 



This Chiton is neither exactly described nor correctly figured 

 in the " Perm. Monograph," for if the " diagnosis''' given by Mr. 

 King be correct, several species might be made from the valves 

 that are found at Tunstall. After examining the plates of this 

 Chiton, especially the posterior one, I am inclined to think that 

 the shells included in the genus Metoptoma will prove to belong 

 to the Chitonidce. 



Peculiar to the shell-limestone of the North of England, in 

 which, though not plentiful, it is very generally distributed. 



2. C. HowsEANus, Kirkhy- 



Of this very distinct species Mr. Kirkby has now taken an 

 almost perfect series of plates, and as the original description of 



