464 Mr. 11. Hovvse on the Permian System of the 



merit of the inantJe 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. 



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. 



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

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



34. Calyptr^a antiqua, Howse. PI, IV. figs. 16, 17. — In 

 1847 I found a single imperfect specimen of a patelliform shell 

 at Tunstall Hill, which was described thus in the Tyneside Cata- 

 logue : — 



" Shell small, patelliform, strongly ribbed longitudinally ; mar- 

 gin crenulated ; two deep furrows internally from the apex to the 

 margin, corresponding with tivo strong ribs on the outer surface." 



The only specimen found was not quite perfect round the 

 margin, and the whole shell had the appearance of being irregu- 

 larly gi-own. It was thought, however, desirable to include it 

 in the Permian list, and to affix an epithet to it, for the sake of 

 reference. Mr. King, not being acquainted with it, and conse- 

 quently considering it a "doubtful species,^' placed it in the 

 Appendix to the 'Permian Monograph^ (p. 247), in which posi- 

 tion it has been overlooked by Baron Schauroth, who has been 

 so fortunate, by the discovery of a specimen [Patella Hollebeni) 

 from the lowest bed of the Zechstein at Ilmenau, as to be able 

 to confirm the certainty of its existence in the Permian system. 

 As Baron Schauroth's specimen was more perfect than the one 

 described above, it seems advisable to extract a portion of his 

 description, which, so far as it can be compared, agrees with 

 the present species : — 



" The first, and at present the only known Patella of the Per- 

 mian system has an elliptical (marginal) outline, which is slightly 

 narrower in that part of the shell in which the elevated apex 

 occurs, so that it is rather oval. The apex is situated in a third 

 part of the length of the shell, and its height bears a proportion 

 of one-third to the whole length of the shell. The surface is 

 covered with fine, crowded, concentric, raised lines, which dis- 

 appear almost entirely at the apex. The latter are crossed by 

 gradually enlarging, radiating lines from the apex, so that the 

 whole of the surface is cancellated or cut up into wire-work 

 markings." 



The only known English example is from the shell-limestone 



