46 CIDARIS 



Affinities and differences* — This species most nearly resembles C. clavigera, Konig ; it 

 is distinguished from that species, according to Professor Forbes, by having " the ambulacral 

 segments slightly broader in proportion to the inter-ambulacrals, and instead of their 

 breadth being occupied by transverse series of about four granular tubercles, two of which 

 are very small and inconspicuous, there are four, or, centrally, even six, nearly equal 

 granular tubercles in each transverse row. The large spinigerous tubercles of the ambu- 

 lacral plates are placed in areolae, much smaller in proportion to the entire body than in 

 C. clavigera, and the tubercles themselves are also smaller. The spaces between the 

 rows of spinigerous tubercles are wider ; they are thickly studded with nearly equal 

 granules." 



The spines of C. Bowerbankii resemble those of C. clavigera ; but the club-shaped 

 head occupies the entire stem in the former, whereas in C. clavigera the club-shaped head 

 is carried on the long stem. Compare PI. II, fig. 1, with PL IV, fig. 1 — 3. 



Locality and Stratigram Meal Position. — This species has been found only in the Gray 

 Chalk of Dover. The fine specimen I 'have figured is unique, and belongs to the 

 cabinet of our kind friend Dr. Bowerbank, F.R.S. 



History. — First figured by Prof. Forbes, in Dixon's ' Geology and Fossils of Sussex,' 

 who likewise established the species in that work. The same specimen has been kindly 

 lent by Dr. Bowerbank to figure in this Monograph. 



Cidaris dissimilis, Forbes. PL III, III a, figs. 1 and 2. 



Cidaris sceptrifera, Forbes, in Dixon's Geology of Sussex, pi. xxv, fig. 3. 



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



— — Woodward. Mem. Geol. Snrvey, Decade v, expl. pi. v. 



Test small, depressed, ambulacral areas narrow, flexuous, with six rows of small 

 granules ; inter-ambulacral plates, four to five in a column ; areolae circular, wide apart, 

 surrounded by distinct secondary tubercles ; principal tubercles prominent, bosses slightly 

 crenulated, the inferior oral tubercles minute, the uppermost discal, rudimentary, and 

 without areolae ; miliary granules large and prominent ; spines slightly fusiform, surface 

 covered with longitudinal lines of prickles. 



Dimensions. — A. Transverse diameter eleven lines ; height six and a half lines. 

 B. Transverse diameter, one and one fifth inches. 



Description. — This urchin resembles Cidaris sceptrifera in its general characters, but 

 was separated from that species by Professor Forbes in his MS. notes on this Cidaris. 



