FROM THE GREY CHALK. 43 



Mant., of the White Chalk, by having fewer tubercles in the columns, which are wider 

 apart in the upper portion of the test ; the areolas are likewise shallower, and the border 

 more prominent. In Cidaris scepMfera the tubercles are largely developed (PI. VI, VII), 

 with deep areolas surrounded by a circle of prominent granules, and with a narrow sinuous 

 miliary zone. The spines likewise are large and fusiform, having their surface covered with 

 prominent spiny granules. Cidaris vesiculosa, Goldf., differs from C. subvesiculosa, d'Orbig., 

 in having the test flatter, the tubercles smaller, less numerous, and more apart. 



The specimens of this urchin, collected from the Upper Greensand of Wiltshire, were 

 by the late Professor Forbes^ referred to Cidaris insiffiiis, Gras. Through the kindness of 

 my friend W. Cunnington, Esq., F.G.S., I have been enabled to examine the beautiful 

 series of this species in his collection, and in PI. II, fig. 5, have figured his largest and 

 finest specimen. A careful study of these fossils has satisfied me that they are not the 

 species described by Dr. Albin Gras,' and which he thus characterized : — " Aires ambula- 

 craires ondulees, paraissant presenter deux rangees verticales de granules tres serrees et 

 rapprochees les unes des autres ; probablement cinq tubercles inter-anibulacraires non 

 creneles dans chaque rangee (quatre paraissent seulement dans notre exemplaire, dont la 

 partie superieure n)anque). Sur les cinq tubercles, les trois inferieurs augmentent pro- 

 gressivement de grandeur en allant de bas en haut ; leurs scrobicules et leurs cercles scro- 

 biculaires ronds, saillants et formes de granules serres, sont tres-prononces, tangents entre 

 eux et avec ceux de la rangee voisine ; ils sont au contraire presque effacee dans le petit 

 tubercle qui vient ensuite, lequel diminue brusquement et repose pourtant sur une tres- 

 large plaquette couverte de norabreux granules." The ambulacral areas in C. vesiculosa, 

 Goldf., have, at the equator, six rows of small, equal-sized granules, closely arranged in 

 parallel lines, and diminishing to four rows at the narrowest parts. This persistent 

 structure affords a character by which the species is distinguished from C. insignis. 



The British Museum contains a fine specimen of C. vesiculosa, G(M.L, from the Gray Chalk 

 of Dover (PL III, fig. 1). This test I have carefully compared with Mr. Cunnington's 

 Upper Greensand specimens, and the examination has convinced me that they belong to 

 the same species ; the test of the specimen from the Gray Chalk is that of a larger, and 

 older individual; some of the plates, however, in the upper part of the columns, are 

 proportionally more inflated ; but in all other respects its characters are identical with 

 those of the Upper Greensand forms. 



The test is spheroidal, of medium size, and nearly equally depressed at both poles ; the 

 ambulacral areas form narrow, flexuous, granular bands, which decline towards the 

 central suture ; they are entirely filled with small, close-set, equal-sized granules, arranged 

 in regular parallel rows, of which there are from six to eight at the equator, diminishing 

 to four in the narrowest parts, near the peristome and apical disc ; the poriferous zones 



1 Morris, ' Catalogue of British Fossils,' 2ncl ed., p. 74. 



2 'Description des Oursins Fossiles du departemeiU de I'ls^re,' p. 21, 1848. 



