FROM THE GREY CHALK. 45 



been collected only from the Gray Chalk of Dover and the Upper Greensand of Wilts. 

 Cidaris vesiculosa, Forbes, is a very different form from the true C. vesiculosa, Goldf. ; and I 

 must refer the reader to the article on that species for more ample details. This species 

 has been beautifully figured and well described by M. Cotteau, both in his Monograph on 

 the Echinidse of Sarthe, and his continuation of D'Orbigny's Echinides de Terrains 

 Cretaces, in the Paleontologie Fran9aise, a work which has profited so much by M. Cot- 

 teau's extensive knowledge of this subject. This species has now been identified and 

 figured as British for the first time. 



Cidaris Bowerbankii, Forbes. PI. II, fig. 1, a — d. 



Cidaris Bowerbankii, Forbes, in Dixon's Geol. and Fossils of Sussex, pi. xxix, fig. 4, 



p. 330, 1850. 

 — — Forbes, in Morris's Cat. of Brit. Foss., 2nd ed. p. 74. 



« 



Test spheroidal, depressed, ambulacral areas with four or six rows of nearly equal- 

 sized granules ; inter-ambulacral areas wide, five or six large spinigerous tubercles, with 

 small areolae in each column; miliary zone wide, filled with small, close-set, 

 equal-sized granules. Spines very large, thick, and inversely conical, stems short, the 

 surface covered with irregular, longitudinal rows of granulated spines. 



Dimensions. — Transverse diameter one inch ; height unknown. 



Description. — The body of this Cidaris, which is very nearly allied to C. clavigera, is 

 more compressed above and below than in that species. 



The ambulacral areas are occupied by four or six small, nearly equal, granular 

 tubercles in each transverse row, and the poriferous zones are narrow and slightly 

 sinuous. 



The inter-ambulacral areas are wide ; the spinigerous tubercles, five or six in each 

 column, have small areolae, without prominent margins ; the miliary zone is flat, and 

 undepressed ; and the entire surface is thickly covered with minute nearly equal-sized 

 granules, of which a circle of larger ones surround the border of the areolae. 



The primary spines, seen in situ on the test (fig. 1, a), are thick, almond- 

 shaped, inversely conical bodies, with a short neck, into which the body suddenly 

 contracts (fig. 1, b) ; the milled ring is broad and prominent (fig. 1, c), and the acetabulum 

 has a narrow rim close to the ring ; the surface is minutely granulated with small spinous 

 points, arranged in regular longitudinal rows (fig. 1, b) ; the spines which clothe the 

 granular tubercles are small, compressed, conical bodies, with a striated surface (fig. \,d); 

 several of these are found in situ on the plates of the test. 



