BRITISH FOSSILS. 



Decade Y. Plate Y. 

 cidaris carteri. 



[Genus CIDARIS. Klein, 1734. (Sub-kingdom Radiata. Order Echinodermata. 

 Family Cidarida;.) Body sphaeroidal ; ambulacra narrow, undulating, with two or more 

 rows of miliary granules only ; pores in single file ; iuterambulacral segments very broad, 

 with two rows of primary tubercles, few in number, the uppermost often rudimental ; 

 interspaces of the areolae densely granulated ; apical disk large, of 5 large genital and 

 5 ocular plates, round a pentagonal anal area minutely plated ; oral opening round, 

 simple, its disk composed of small imbricating plates. Primary spines few and large, 

 ail the rest small and flattened.] 



Diagnosis. C. parva, subconica, ambulacris bigranulcttis longitudinaliter 

 sulcatis; tuberculis inter ambidacr or um conspicuis remotis — areolis omnibus 

 parvis, superioribus elongatis, obsoletis. 



Eeferences. C. Carteri, Forbes (1854), in Morris's Catal., 2nd edit, 

 p. 74. Desor (1854), Synopsis des Ech. Foss. p. 12. 



Description. — Cidaris Carteri is tlie smallest species of the genus 

 found in the English chalk ; the specimen represented, though 

 apparently adult, only measures 10 lines in diameter and 8 in 

 height. It is like a minature of the well-known C. sceptrifera^ 

 from which it differs chiefly in the more conical form, and in the 

 less development of the areolae in the uppermost plates. The 

 ambulacra have only two distinct and two indistinct rows of 

 granules, whereas the adult G. sceptrifera has four distinct and 

 two indistinct rows. The primary tubercles are perforated, but not 

 erenulated, and the areolae are deeply sunk and surrounded by a 

 rather conspicuous circle of mamillated granules. The apical plates 

 are less roughly and densely granulated than in C. sceptrifera, and 

 the oculars are relatively much smaller. 



Locality and Geological Position. — The only specimen at present 

 known is in the collection of James Carter, Esq., of Cambridge, 

 who obtained it from the Lower Chalk of that neighbourhood. In 

 [v. v.] 5 E 



