13 



observable. The form of the one is rather orbicular and depressed, and 

 of the other somewhat conoidal : in the one are no papillae, whilst in the 

 other they are well preserved. Leske, who has remarked the difference 

 very correctly, explains it, in part, by considering the latter as a silicious 

 cast : a circumstance which fully accounts for the absence of the papillae; 

 but the difference of their form remains unaccounted for. An exami- 

 nation, however, of the fossils figured Plate I. Fig. 9 and 11, will, I 

 think, show that this difference is only to be explained, by supposing the 

 two fossils to be of two distinct species, or at least varieties. 



In the echinite from Oxfordshire, of a globose form, Plate I. Fig. 9, 

 the narrow strip of area, edged by the ambulacra, is formed by four 

 rows of small and equal sized granular tubercles ; whilst in the other, 

 Plate I. Fig. 11, from Kent, these areolae are wider; and, except 

 towards their superior and inferior extremities, are composed of six rows 

 of granular tubercles, which are large in the external rows, and dimi- 

 nish as they approach the centre. Its papillae, though perforated in 

 the apex, are not crenulated at the base. The much greater space of 

 granulcited area between the papillae, and the conoidal form of the 

 shell, also help to constitute a difference so great, as to lead to the 

 opinion, that it should be considered as a distinct species. If this 

 should be admitted, the species might be distinguished as cidaris papillata 

 conoidea. 



The echinite from Wiltshire, Plate I. Fig. 6, beautiful from its origi- 

 nal formation, and estimable as a fossil, from its state of preservation 

 being such, that even somewhat of the original colour of the shell is still 

 to be perceived, partakes so much of the characters of C. mammillata 

 and papillata, as to render it difficult to determine with which it should 

 be arranged. Like the former, its less areae equal half the width of the 

 larger, both being ornamented with papillae of a proportionate size; but, 

 like the latter, its papillae are perforated in the apex, and crenulated at 

 the base; and this is the case even with those papillae which are disposed' 

 on the Less areae. The pores of the ambulacra, as in the former, dirni- 



