242 ON THE PERMIAN CHITONID^. 



Sandberger,* Prof. De Koninck,"!" Baron De RyckholtjJ and 

 Dr. Roemer.§ To De Ryckholt and De Koninck more especi- 

 ally the palaeontology of this interesting group is greatly indebted. 

 A little difference seems to exist as to the true number of species 

 that have been discovered in these rocks . The latter states that 

 there are seven Carboniferous and four Devonian species; but, 

 should we agree with De Ryckholt, the list would be increased 

 by the addition of seven to the Carboniferous list. 



It may therefore be supposed that our knowledge of the Chi- 

 tonidce of the British Palaeozoic rocks is somewhat imperfect, as 

 may also be said of our acquaintance with the fossil members of 

 this family generally. It is evident that it was not sparingly 

 represented during palaeozoic eras; for the distribution of its 

 species in the Durham Permian beds, and their greater distribu- 

 tion in the Carboniferous rocks of Belgium, demonstrate that so 

 early as the epochs of these systems the group held an important 

 position in marine faunas. When six species are found in one 

 Permian locality, and seven in a small district of the Carboni- 

 ferous strata, it may readily be inferred that their absence or 

 scarcity in other strata, and systems of strata, can hardly be due 

 to a general paucity of representatives. The fragmentary state in 

 which fossil Chitons usually occur, and the obscurity which 

 shrouds the affinities of some of the species, owing to the resem- 

 blance of their plates to the shells of the Patelliform Gasteropods, 

 may have caused false determinations in some instances, at the 

 expense of their numerical appearance. Both Prof. King || and 

 Mr. Howse*[[ have suggested the possibility of the somewhat ob- 

 scure Carboniferous species constituting the genus Metoj)toma 

 belonging to this family ; and the great resemblance of the plates 

 of some of the palaeozoic members of this family lends force to 

 the suggestion. For instance, what could more resemble a Pa- 



* Neues Jalirb. fiir Mineral, u. s. w., 1841, p. 240, and 1842, p. 399. 

 t Descript. des anim. foss. du terr. carb. ; and Bull, de I'Acad. Koyale de Bclg., 2mc 

 s^ric, tome ili., no. 11. 

 X Bull, de I'Acad. Koyale de Belg., tome xii., no. 7. 

 § W. Duuker u. II. v. Meyer, Pala^ontographica, tome v., p. 36. 

 II Ann. & Mag. Nat. Hist., 1 ser., vol. xiy., p. 382. 

 ^ Trans, of Tyneside Nat. Field Club, vol. iii., p. 272. 



