ECHINODERMATA. 31 



Cidaris Ilminstjsliensis, Wright, n. sp. PI. V, fig. G a, b. 



Test large, form unknown ; ambulacral areas narrow, with two marginal rows of small 

 granules ; poriferous zones narrow, pores nearly round, and closely approximated ■ inter- 

 ambulacral plates large, as deep as they are wide ; areolas large, circular, surrounded by 

 a complete scrobicular circle of small granules; mammary bosses not much elevated; 

 summits deeply crenulated ; tubercles of moderate size. 



Description. — We only possess, of this species, one tubercular plate, and a portion of 

 a second, with one half of the corresponding part of the ambulacral area, but still this 

 fragment is sufficient to enable me to give its diagnosis, and point out those characters by 

 which it is distinguished from its congeners. The test must have attained a size quite 

 equal to that of Cidaris Fowler i ; the ambulacral areas are very narrow, and have only 

 two rows of marginal granules, there being one granule on each alternate plate; the 

 poriferous zones are narrow, the holes are contiguous and nearly round, and each pair has 

 a thin septum separating them (PI. V, fig. 6 b) ; there are fifteen pairs of holes opposite 

 each large inter-ambulacral plate. 



The inter-ambulacral areas are composed of large, nearly quadrate, tubercular plates 

 (fig. 6 b) ; the number of the primary tubercles is unknown ; the areolas are large and 

 circular, and are surrounded by a scrobicular circle, composed of very small granules 

 (fig. 6 b) ; down the inter-tubercular space there were other four rows of granules of nearly 

 the same size ; the scrobicular circle extends so very near to the poriferous zones, that there 

 is no granular space intervening between them (fig. 6 b); the mammary boss is not 

 very prominent, but its summit is sculptured with well-defined crenulations ; the tubercle 

 is of moderate size, and has a wide perforation in its summit. 



Affinities and differences. — This species differs from Cidaris Edwardsii in having a 

 complete scrobicular circle of granules around the areolas, in the narrowness of the ambu- 

 lacral areas, with only two marginal rows of granules, and in the scrobicular circle abutting 

 against the poriferous zones without a row of granules separating them ; the smallness of 

 the holes in the zones, and their proximity to each other, is another point of difference. 

 Compare PI. I, fig. 1 b, with PI. V, fig. 6 b. 



Cidaris Ilminsterensis differs from Cidaris Fotvleri in having no granules between the 

 scrobicular circle and the zones, the latter having two or three rows (fig. 4 e, PI. I) ; the 

 breadth of the ambulacra, and its four rows of granules, and the wide poriferous zones, 

 with the holes kept far apart by very thick septa, serve further to distinguish that 

 Inferior Oolite form from this Upper Lias species. 



Locality and Stratigraphical position. — It was collected by Mr. Moore in the Upper 



