256 ON THE PERMIAN CHITONID^. 



plates are found in the same neiglibourliood, and it is not un- 

 common to find a more or less perfect series in pretty close conti- 

 guity. The plates of C. Hancockianus were associated with those 

 of the present species ; and they compose a mixed set ; and so 

 with the other fossils which occurred along with the remains of 

 the Chitons. Those species composed of a plurality of parts 

 were always represented by their different members ; for instance, 

 the remains of a species of Cldaris were found in fragments, 

 but they included its plates and spines, though of very different 

 gravities ; also the remains of a Crinoid in a multiplicity of pieces, 

 but amongst them occurred the component parts of its stem, cup, 

 and arms. Indeed the whole of the evidence deducible from 

 the conditions of the various fossils found in this particular area 

 of the Tunstall limestone seems to indicate that they are remains 

 of the original inhabitants of the calcareous bed, and not the 

 sweepings of a current from other regions. So that, in consi- 

 dering the ten plates of C. antiquus to have been distributed 

 generally over the mantles of the individuals to which they be- 

 longed, I adopt an opinion that is borne out by their manner 

 of occurrence, and of that of the associated fossils, as well as by 

 analogical evidence from the observed distribution of other Per- 

 mian Chitonidce. 



Mr. Howse discovered the first specimen of this species. His 

 plate was imperfect about the margin; consequently he did not 

 detect its process of insertion. He therefore somewhat natu- 

 rally mistook his new fossil for a species of a Calyptrcea ; and in 

 his " Catalogue of Permian Fossils," published in 1848, it is de- 

 scribed under the name of Cal. antiqua, as follows : — " Shell 

 small, patelliform, strongly ribbed longitudinally ; margin crenu- 

 lated ; two deep furrows internally from the apex to the margin 

 corresponding with two strong ribs on the outer surface.''* The 

 " two deep furrows" which he notices as characterising his plate 

 internally must have been an accident of growth ; for similar fur- 

 rows have not been observed in any of the plates subsequently 

 found. A notice of this discovery appeared in the Appendix of 



♦ Cat. rerm. Fo.ss., p. 24. 



