44 CIDARIS 



ai'e very narrow, and the small pores are placed close together, each septum being sur- 

 momited by a little granule; there are 23 pairs of holes opposite one of the large plates. 



The inter-ambulacral areas are formed of large deep plates, the limits of which are 

 very distinctly defined by well-marked sutural lines ; there are four or five plates in each 

 column, those at the lower part of the test are small and regular (fig. 1, b), and those at the 

 upper part of the column are large, deep, and rather irregidar in figure, from the extreme pro- 

 minence of the areolar margin (fig. 1, a, c); each plate, with the exception of the uppermost 

 in each alternate column, supports a large primary tubercle ; it is surrounded by a shallow 

 circular areola ; the boss is not prominent ; and the summit is smooth, without a trace of cre- 

 nulation ; the tubercle is large, sessile, and perforated (fig. \, e); the margin of the areola is 

 very prominent, which, in the larger plates especially, produces an inflation of their surface, 

 and probably suggested the specific name vesiculosa (fig. \,a). A complete circle of mammil- 

 lated granules, larger than those on other parts of the test, surrounds the margin of the areolae, 

 and forms a prominent boundary thereto (fig. 1, d). The uppermost plate in each alternate 

 column, in most specimens, is either destitute of a tubercle, or represented only by a rudi- 

 mentary warty body, without areola, and situated in the midst of a long, narrow, 

 imperfectly developed plate, on all sides surrounded by granules. 



The mouth is small and circular, and of the same diameter as the aperture for the 

 apical disc, which is likewise entirely circular. 



Locality and Strafiffraphical Position. — The specimen figured in Plate III, fig. 1, be- 

 longing to the British Museum, was collected from the Gray Chalk, at Dover, and the one 

 figured in PL II, fig. 5, belongs to my friend W. Cunnington, Esq., F.G.S., Devizes, and was 

 obtained from the Upper Greensand of Wilts. The specimen in my own collection is 

 from the Gray Chalk of Dover. I believe this urchin is very rare, as I have seen very 

 few specimens in the different collections of Cretaceous fossils. The Rev. T. Wiltshire, 

 F.G.S., has communicated a fragment, collected from the Red Chalk of Hunstanton Cliff, 

 together with three detached spines, of the same species. 1 am inclined to refer to this 

 species the specimen, figured in PI. Ill, fig. 3, collected by C. B. Rose, Esq., F.G.S,, 

 from the Red Chalk, and kindly communicated for this work. The test is much defaced 

 by friction, but still many of the more remarkable characters of the urchin are well 

 preserved. 



History. — This urchin was figiu-ed and described for the first time by Goldfuss, from 

 some isolated plates and spines collected from the creta margacea of Westphalia; that 

 author cites, as identical with Cidaris vesiculosa, a fragment from the White Chalk of 

 England figured by Parkinson, but which belongs to another species, probably Cid. 

 perornata, Eorb. This error has led to much confusion, for we find Cid. vesiculosa, Goldf., 

 cited in many English lists as having been obtained from the White Chalk of Kent, Sussex, 

 and Wilts ; whereas the new form now figured and identified with Goldfuss's species has 



