FROM THE UPPER CHALK. 135 



CiDARis cOEOLLAKis, Morris. Catalogue of British Fossils, p. 49, 1843. 



— SAXATiLis, Morris. Ibid., p. 50, 1843. 



CypHOSOMA COKOLLAKE, Agassiz et Desor. Catal. Rais. des Echinides, p. 351, 1846. 

 CiDARis coEOLLARis, Bronn. Index Palseontologicus, p. 298, 1848. 



— SAXATILIS, Bronn. Ibid., p. 300, 1848. 



Cyphosoma corollare, TfOrUgny. Prodrome, t. ii, p. 273, Et. 22, 1850. 



— — Forbes. In Dixon's Geol. of Sussex, p. 340, 1850. 



— — Forbes. In Morris's Catalogue of Brit. Foss., p. 75, 1850. 

 Phymosoma — Desor. Synop. des Echinides fossiles, p. 88, 1856. 

 Cyphosoma saxatile, Desor. Ibid., p. 87, 1856. 



— COROLLARE, Pictet. Paleontologie, 2e ed., t. iii, p. 243, 1857. 



— — Woodward. Mem. Geol. Surv., Decade V, p. 2, 1858. 



— — Leymerie et Raidin. Ge'ol. du Depart, de I'Yonne, p. 621, 



1858. 

 Phymosoma saxatile, Diijardin et Hupe. Hist, des Echinoderm., p. 508, 1862. 



— COROLLARE, Dvjardin et Hupe. Ibid. 

 Cyphosoma perfectlm, Cotteau et Triger. Echinides de la Sartlie, p. 261, pi. xlii, 



figs. 13—16, 1860. 



— — Cotteau. Echinides foss. des Pyrenees, p. 24, 1863. 



— COROLLARE, Cotteau. Pal. Fran^aise, t. vii, p. 669, pi. 1165, 1864. 



Test small, circular, depressed ; ambulacra wide, two rows of tubercles, nine to ten in 

 each, gradually diminishing in size towards the poles ; inter-ambulacra moderate, with two 

 rows of tubercles, nine in each, four ambital, large ; areolae defined by rows of granules ; 

 miliary zone moderate, granular below, becoming smooth above ; poriferous zones narrow, 

 undulated, pores unigeminal, and crowded near the summit ; base concave ; oral opening 

 small, one third of an inch in diameter ; discal opening large, pentagonal, half an inch 

 in diameter ; spines long, slender, spatulate, one fom'th longer than the diameter of the 

 test. 



Dimensions. — Transverse diameter one inch ; height one third of an inch ; in general 

 the specimens are not so large. 



Description. — This is one of our most common Cyphosomuta. In certain localities it is 

 a small, circular Urchin, rarely exceeding an inch in diameter and about three or four 

 lines in height ; it is convex and depressed above, and flat or subconcave below ; the areas 

 are nearly equal in width, the tubercles very much alike in form and size, the areolae are 

 encircled with granules, and the structure of the different divisions of the test is very 

 uniform throughout. 



The ambulacral areas (PI. XXVI, fig. 10), contracted above by the poriferous zones, 

 have two rows of primary tubercles supported on large bosses, and arranged in alternate 

 series on each side of the area ; in adult specimens there are nine or ten tubercles in a 

 row ; the areolae are wide, and a single row of graimles (rarely double) separates them 

 from each other. 



The poriferous zones are narrow, and much undulated at the ambitus and infra-mar- 



