| Fig. | 1.— | Hemicidaris intermedia; view in profile, showing the teeth projecting: 1/3 nat. Calne. |
| 2.— | The same seen from above, displaying the outlet, and surrounding pores. | |
| 3.— | The same, view of the base, displaying the mouth, surrounded by five angular bipartite teeth. The ambulacral tubercles at the base are omitted in the figure. | |
| 4.— | Diadema rotulare (Agass.): viewed in profile: not. | |
| 5.— | A siliceous cast of another species of Diadema. South Downs. | |
| 6.— | View of the base of Diadema rotulare. This species occurs in the so-called Neocomian Formation of France. |
Cidaris (Hemicidaris?) intermedia,[ Lign. 101, fig. 1, 2, 3].—The shell of this echinite, from the Oolite at Calne, so closely resembles that of H. crenularis, above described. that without the spines it could not be distinguished.[298] It is of a depressed form, and has very long subcylindrical spines; a specimen is figured [Lign. 102, fig. 9]. It is this cidarite which occurs in such immense numbers in the Oolite at Calne, Chippenham, Faringdon, &c. Slabs of limestone are occasionally extracted from the quarries at Calne, with more than thirty of these echinites surrounded by their spines. I have one specimen, attached to a block of limestone, with fifty spines; but it is difficult to detach a perfect spine.
[298] Mr. Woodward. I am indebted to this gentleman for many valuable remarks on fossil Echinoderms.
CIDARIS BLUMENBACHII.
Cidaris Blumenbachii. [Lign. 127, fig. 3.]—This is another beautiful characteristic Turban Echinite of the Oolite. The tubercles are very large and prominent, and the spines remarkably neat, being covered with longitudinal granulated striæ; they are of an elongated cucumerine form, and homogeneous in structure ([Lign. 127, fig. 5]). They occur by hundreds in some of the layers of friable stone in the quarries around Calne.
Many species of Turban Echinites abound in the White Chalk, especially near Gravesend, Northfleet, Purfleet, Charlton, and other places in Kent; the softness of the cretaceous strata in those localities rendering the removal of the chalk an easy task. Splendid specimens, with the spines and tubercles almost as fresh as if recent, have rewarded the patience and skill of collectors. The British Museum contains many fine examples, especially a specimen of Cidaris clavigera from Charlton, with sixteen spines, and the dental apparatus in situ.[299]
[299] Several coloured figures of Cidarites and spines are given in Pict, Atlas, pl. liii. and lvi. A fine series of Chalk specimens are figured in Dixon's Fossils, tab. xxv.; many from the choice cabinet of Henry Catt, Esq. of Brighton.
The collection of Chalk Cidarites with their spines, formed by W. H. Taylor, Esq. F.G.S., of Winterslow-place, Brixton, is the most splendid assemblage of these fossils I have seen.
Diadema. [Lign. 101, fig. 4, 6.]—The shell in this genus is of a more depressed form than in Cidaris; there are two rows of large tubercles, which are crenulated and perforated, on the ambulacra as well as on the interambulacral spaces. The spines are slender and annulated. Mr. Woodward remarks that the common Chalk species referred by authors to this genus, belong to the sub-genus Cyphosoma of M. Agassiz, in which the tubercles are imperforate. There are nearly fifty fossil species known, and they range from the Lias to the Chalk. The recent analogues inhabit the seas of warm regions.