ECHINODERMATA. 41 



proportionate size of its tubercles to that of the test, and in having some of the bosses 

 smooth, and others feebly crenulated, but it is distinctly separated from that form by 

 having six plates in the tubercular columns, Cidaris propinqua having only five ; the test 

 is more globular and inflated, the areolas are smaller, the circles of scrobicular granules are 

 not so prominent, and the tubercles are more crowded together ; the spines of Cidaris 

 Wrightii are larger in proportion to the diameter of the test than in Cidaris propinqua ; 

 their stems are smaller, and taper more, and the rows of tubercles are not very prominent ; 

 whereas in Cidaris propinqua the stems of the spines are thick and elliptical, and the 

 tubercles are large and bead-like on their surface. 



Cidaris Wrightii is distinguished from Cidaris Bouchardii, with which it is associated 

 in the same bed, by its globular and inflated test, the size of the tubercles, and the shal- 

 lowness of the areolas ; Cidaris Bouchardii having a depressed test, with small tubercles, 

 and deeply sunk areolas. 



From Cidaris Fowleri this species is distinguished by the size and prominence of the 

 tubercles, the narrowness of the ambulacral areas and poriferous zones, and the greater 

 proportionate height and inflation of the test • the ambulacral areas in Cidaris Fowleri are 

 broad, with four rows of small granules ; and the pores in the poriferous zones are wide 

 apart. The spines in these two associated species are likewise very different ; those of 

 Cidaris Fowleri are oval, and covered with irregular rows of small spines ; whilst those of 

 Cidaris Wrightii have regular longitudinal rows of small tubercles. 



Cidaris Wrightii has many points of affinity with Cidaris Jlorigemma, both as regards 

 the general structure of its test and the form and decoration of its spines ; but it is 

 distinguished from that Coral Rag form in having larger tubercles and smaller areas, 

 with a much wider granulated miliary zone between the primary tubercles. The 

 spines assigned to Cidaris Wrightii belong to the same group as those of Cidaris Jlori- 

 gemma, but the stem is longer and narrower, and the granules forming the rows are set 

 closer together, and not so prominent as in Cidaris jlorigemma, where they form lines of 

 tubercles very distinct from each other. Although connected by delicate calcareous threads, 

 the apices of the tubercles are likewise directed forwards, and the summit of the stem 

 terminates in a truncated star-like extremity. (PI. I, fig. 3 e.) 



Locality and Strati graphical position. — This is a very rare Cidarite. Three specimens 

 only have been found by me in the Pea Grit of Crickley Hill, which are all more or less im- 

 perfect ; and I have never seen an example in any other cabinet. An urchin found in 

 the Stonefield Slate at Eyeford, Gloucestershire, is referred to Cidaris propinqua. Whether 

 this is identical with Cidaris Wrightii I have no means of judging, not having seen 

 the type specimen catalogued under that name. 



History. — It was first figured in my ' Memoir on the Cidaridas of the Oolites,' and 

 subsequently entered in M. Desor's ' Synopsis des Echinides ' under the name it now bears. 



G 



