[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.
Echinus.--The shells of the genus Echinus resemble those of Cidaris in their general structure, but the tubercles are imperforate. More than twenty fossil species are described, from the Oolite and Chalk.
Salenia.--In the greensand pits near Faringdon, in Berkshire, which abound in fossil sponges and other poriferæ (_ante_, p. 228), there are immense numbers of a small elegant Turban Echinite, which belongs to the genus thus named by the eminent zoologist. Dr. J. E. Gray, of the British Museum. The collector will easily recognize these sea-urchins by the plated summit. The shell has five ovarian and five interovarian plates, and an eleventh or odd one. The tubercles are crenulated. The common species at Faringdon is _S. petalifera_, of Desmarest. Two species of this genus, viz. _S. scutigera_ and _S. stellulata_, from near Warminster, are figured in _Pict. Atlas_, pl. liii. _fig._ 12, 13.
_Cidarites of New Zealand._--Detached plates and spines of sea-urchins, belonging to the family Cidaritidæ, have been discovered by Mr. Walter Mantell, in the Ototara limestone of New Zealand; which is a fawn-coloured stone, composed of foraminiferæ, like the Chalk, and containing terebratulæ, corals, and teeth of sharks.[300]