96 M. L. de Koninck on two new Species of Chiton 



Upper Silurian. 



33. Chiton Grayanus, De Kon. Wenlock Limestone, Dudley. 



34. « Wrightianus, De Kon. „ „ „ 



Lower Silurian. 



35. Chiton (Helminthochiton) Griffithii, Salter. Cong, co. Galway. 



On an inspection of this list the result is, that, notwithstand- 

 ing the number is relatively small when compared with that of 

 recent species, the existing genus Chiton is represented in almost 

 alt the series of sedimentary rocks, and that hitherto the Creta- 

 ceous and Triassic are the only formations in which there have not 

 been discovered any traces*. I have no doubt that this gap will 

 soon be filled, as it is not very probable that these animals, 

 whose appearance on our globe dates so far back in geological 

 time as the Lower Silurian, continuing through all the other 

 formations up to the present day, should have been unrepre- 

 sented in these two geological periods. The same list, again, 

 demonstrates that, after the Tertiary, it is the Carboniferous 

 strata which contain the greatest number of species, and that it 

 is the intermediate strata which have furnished the fewest f. 



I shall now proceed to give descriptions of the two new species 

 of Chiton which form the principal subject of this notice. With 

 the specimens of one I have been aided by Mr. John Gray of 

 Hagley, by whom it was discovered, and of the other by Dr. 

 Thomas Wright of Cheltenham, well known for his investigations 

 upon the fossil Echinoderms of Great Britain. 



1. Chiton Grayanus, De Koninck. (PL II. fig. 1 a, b, c,d.) 



The dorsal cerames, or intermediate plates of this species, 

 which are the only ones with which I am acquainted, are formed 

 of two lateral parts, perfectly plane, of a nearly square form, and 

 united together by an angle a little more than a right angle. 

 The dorsal carina is most developed ; the anterior part of each 

 plate is slightly crenated ; the test appears to have been very 



* Mr. Charles Moore's discovery of Triassic Chitons in British strata 

 was made since the publication of Professor De Koninck's paper. See 

 note § on page 94. 



t While this article was in the press, Mr. Charles Moore has favoured 

 me with the additional information of his having found examples of the 

 genus Chiton in the following formations in England, in which they had 

 not hitherto been observed, viz. : — 



Bradford Clay ; Hampton, near Bath : a single plate. 



Upper Lias ; near Ilminster : about a dozen separate plates, all belong- 

 ing to one species. 



And in the Triassic beds near Frome, before alluded to, where the plates 

 of a small and not uncommon species occur. — W. II. B. 



