FROM THE WHITE CHALK . 53 



valleys between the ridges are concave, and the surface of these is very finely granulated ; 

 the neck is long and smooth (fig. 1,/, and fig. 2); it is bounded by a fine line, and 

 beyond this is a narrow circle with microscopic lines conducting to a milled ring, which is 

 prominent and finely sculptured (fig. \,f, and fig. 2); the head is small, and the rim of 

 the acetabulum striated; the small secondary spines are flat and conical (fig. 1, li), and 

 have the surface ornamented with fine longitudinal lines. 



Affinities and Differences. — This species is allied to Cidaris vesiculosa, Goldfuss, but 

 distinguished from that form by having the test more regularly convex, the plates of 

 the inter-ambulacra less inflated, and fewer tubercles in each series. The spines of the 

 two species are likewise different. It resembles Cidaris sceptrifera, Mantell, but has smaller 

 areolas, less prominent scrobicular circles, fewer tubercles in each column of plates ; and the 

 spines are very distinct (compare for example PI. VII, fig. 1, with PI. XI, fig. 1 ). According 

 to Professor Forbes, it differs from Cidaris snhvesicuhsa, d'Orbigny, in having the inter- 

 ambulacra composed of large plates with impressed areolae around the spiniferous 

 tubercles, four to six in the perpendicular row. Tubercles larger in proportion to the 

 areolae than in the last species. Superior plates with indistinct tubercles, but not so 

 obsolete as in C. subvesicidosa. Granulated portion of the plates finely grained ; the 

 sutures are not impressed ; the avenues of pores, of which about fourteen correspond to 

 the largest plate, are broader in proportion to the ambulacra. There is a tubercle 

 between each pore, and an oblong transverse ridge between each pair. 



Locality and Stratigraphical Position. — I collected, about twenty years ago, a 

 specimen of this urchin with the spines attached to the test, in the Upper Chalk, at Lewes, 

 in Sussex ; the example of this species figured in Dixon's work was obtained from the 

 same locality. The fine fossil which I have figured in PI. XI, fig. 1, was kindly com- 

 municated for this Monograph by Henry Willett,Esq.,F.G.S., Brighton. This specimen 

 appears to be the original fossil which was figured before by Sowerby in Dixon's ' Geology 

 of Sussex ;' if so, it formed the subject of Professor Forbes' observations. 



In France this urchin is very rare ; it was found in the Etage Senonien at Civieres, 

 Giverny (Eure) ; Royan (Charente-Inferieure). 



History. — This species was first well figured as Cidaris serrifera by Professor Forbes 

 in Dixon's ' Geology of Sussex' in 1850. The same year M. I'Abbe Sorignet described 

 it under the name C. punctillum in his work on the Fossil Urchins of the Department of 

 the Eure ; as this account was not accompanied by a figure, I have retained the name 

 of the figured specimen. In 184. "3, Prof. Reuss figured this Cidaris in liis fine work on 

 the Fossils of the Bohemian Chalk-formation, and erroneously referred it to Cidaris 

 claviyera, Konig, from which it differs in many important details both in the structure 

 of the test and spines. 



