FROM THE GREY CHALK. 39 



Cidaris clavigera, Konig, both in the form of the tubercles and the narrowness and depth 

 of the areolae ; but in the structure of the spines there is a manifest difference, which will 

 be more fully appreciated by comparing PI. IV, fig. 1, exhibiting a series of spines of 

 C. clavigera, with PI. II, fig. 3, b, showing a magnified view of the spine of C. velifera. 



Locality and Stratigraphical Position. — W. Cunnington, Esq., F.G.S., of Devizes, to 

 whom I am indebted for the loan of specimens of this species, obtained them from the 

 Upper Greensand near Warminster ; I had seen the plates of the test and portions of the 

 spines, but never before have I seen these parts " in situ. 5 ' 



The foreign distribution of this urchin is as follows : — The spines are found in the 

 Craie chloritee of Essen, Prussia, and of Frohnhausen, Hesse-Cassel, and the test, 

 described under the name Cidaris Heberti, Des., was collected from the Craie de 

 Vendome, from the Craie chloritee du Cap la Heve and la Madeleine, near Vernon 

 (Eure) in l'Etage Cenomanien, where it is very rare. 



C. — Species from the Greg Chalk. 



Cidaris Carteri, Forbes. PI. I, fig. 1, a, b, c, d, e,f. 



Cidaris Carteri, Forbes. Memoirs of the Geol. Survey, Decade v, pi. v, 1854. 



— — Morris. Morris's Catalogue of Brit. Fossils, 2nd ed., p. 74, 1856. 



— — Desor. Synopsis des Echinides Fossiles, p. 12, 1858. 



Test small, inflated, subcorneal; ambulacral areas narrow, winding, with two marginal 

 rows of moniliform granules, and a deep median sulcus ; inter-ambulacral areas wide ; 

 tubercles small, remote ; areola? at the equator narrow, complete, those on the upper plates 

 small, elongate, and obsolete. 



Dimensions. — Height, eight lines ; transverse diameter, ten lines. 



Description. — Should subsequent discovery confirm the opinion that this is an adult 

 test, it will be the smallest Cidaris in the English Chalk. It very much resembles, in 

 many points of structure, Cidaris sceptrifera, Mant., from which it differs, however, in 

 size and figure, and in the development of the tubercles and their areolae, especially those on 

 the upper plates. The ambulacral areas are narrow and winding ; they have two rows of 

 prominent moniliform granules on the extreme margins of the areas (fig. 1, c) ; and in the 

 depth of one equatorial inter-ambulacral plate I have counted sixteen of these ; between 

 them is a deep sulcus, on which two indistinct central rows of microscopic granules are 

 sparsely distributed. 



