2 



BRITISH FOSSILS. 



sentations of Bourguet and Knorr should be referred. But the figure in 

 Parkinson's " Organic Remains " (PI. XLIIL, fig. 6) of a " mammillated 

 echinite from Wiltshire," unquestionably represents the species under 

 consideration, though usually quoted as identical with the crenularis of 

 Agassiz. The figure in PI. IV., fig. 20, of the same work, repre- 

 senting a Wiltshire fossil with its spines, seems to me to belong to this 

 species also, though it does not appear to have been cited as such 

 except by Phillips in his " Geology of Yorkshire." In Dr. Fleming's 

 " History of British Animals," the name Cidaris intermedia is applied 

 to the former figure. Now as Lamarck expressly mentions that his 

 Cidaris crenularis came from Switzerland, and as the Hemicidaris 

 crenularis of Agassiz may fairly be regarded as that species, whilst it 

 has been fully described and figured, and is certainly distinct from 

 the British one, I propose to use Fleming's name of intermedia for the 

 latter, and leave crenularis to that of Agassiz; thereby confusion 

 will be avoided in future. Dr. Mantell has copied the figure of the 

 Swiss species in his " Medals of Creation," vol. i. p. 340, remarking, 

 however, that though usually identified with Parkinson's, he had never 

 seen specimens in the English oolite like that figured by Agassiz. 



Hemicidaris crenularis is sub-globose, varying from a depressed spheroid 

 to a barrel-like shape. Its surface is elegantly studded with very pro- 

 minent and large bosses bearing on their crenulated summits the perforate 

 spiniferous tubercles. The ambulacral areas are very narrow at their 

 summits, but gradually widen out in their course downwards, and 

 immediately at the margin of the mouth are equal in diamej;er to the 

 buccal ends of the interambulacral spaces. The latter are widest in 

 their centres, and gradually narrow towards each end. Each inter- 

 ambulacral area is occupied by two rows of tubercles, each row in- 

 cluding from six to eight, and as there is one of these tubercles on each 

 interambulacral plate, the total number of plates in each area is from 

 twelve to sixteen. Each plate is mainly occupied by the boss and its 

 areola, the latter being quite smooth, and occupying less than half of 

 the width of the former, which is also smooth, distinctly separated from 

 the areola, very prominent, and depressed on its summit, where it 

 is strongly crenulated around the base of the spheroidal deeply- 

 perforated spiniferous tubercle. The tubercle is in diameter rather 

 more than the breadth of the areola. The areolated spaces of the 

 several plates are confluent ; consequently on the upper and lower 

 edges of the interambulacral plates there are no granules. But along 

 the edges of both sides of each plate, there is a conspicuous row of small 

 but well-marked perforated secondary tubercles, partially separated from 

 each other by one or two granules. There are seven or eight of these 

 on each edge of the larger plates. This produces the effect of a 



