FROM THE RED CHALK. 79 



spines, which do not exactly agree with those previously referred to in this Monograph ; 

 four of these are drawn on PL XH, of which figs. 7, 8, and 9 are from Hunstanton, and 

 fig. 1 from Speeton. They may be divided into three classes — (a) slender, having few (ten 

 to sixteen) longitudinal ridges, with a prickly border, PL XH, figs. 7 and 9 ; (|3) thick, 

 having numerous longitudinal ridges, with the prickles almost obliterated, PL XH, fig. 10 ; 

 and (7) slender, without ridges, but with an occasional projecting prickle. 



" The drawing, PL XH, fig. 7, represents a magnified view (the natural size being 

 depicted by a black line) of the expanded extremity of a spine with twelve ridges, not 

 unhke in its general character that to be met with in some forms of the spines of 

 Cidaris Gaultina, but differing from the latter in the valleys between the ridges being 

 covered with very fine longitudinal lines, instead of being marked with fine granulations. 

 Fig. 9, with ten ridges, is marked also by the fine longitudinal striae, and the absence of 

 granulations in the valleys ; the lines of spiny projections or prickles are thinner, more 

 conspicuous, sharper, and less numerous than in the spines of C. Gaultina; it is very 

 slightly tapering ; the fragment preserved measures an inch in length, and must when 

 perfect have been at least two inches ; in general aspect it bears a strong resemblance to 

 C. subvesiculosa from the Upper Chalk. 



" The spine fig. 10 « (natural size), and fig. 10 (^ (a portion magnified) is found both at 

 Speeton and Hunstanton ; the specimen figured, which was from Speeton, and is not 

 quite perfect, measures one inch and a half in length, and is two tenths at its greatest 

 diameter ; the body of the spine increases very gently in diameter for a short distance 

 from the acetabulum, and then as gently diminishes; the margin of the acetabulum is 

 crenulated, a double milled ring surrounds the head, the neck is short and smooth, and 

 the body is marked by about thirty longitudinal ridges, which are crowned by small and 

 obtuse spiny projections. The valleys between the ridges are covered with fine longi- 

 tudinal striae; the general aspect is that of a spine of C. dissimilis, but the latter 

 generally has the spines much more slender. 



" Fig. 8, from Hunstanton, is only a fragment, half an inch in length, and one tenth of 

 an inch in diameter; it is uniformly cylindrical, with the surface quite smtooli and 

 without striae ; arising from the smooth surface are stout prickles, hke thorns, which are 

 repeated in longitudinal lines at about the distance of the tenth of an inch apart from 

 each other. It is a very pecuhar spine, totally distinct from all those of the Cretaceous 

 species, and mostly resembles the spine of C. perornaia from the Upper Chalk ; in the 

 latter, however, the prickles arise from a small longitudinal ridge, and are not isolated and 

 unconnected. The same form of spine occurs at Speeton. In the ratio of frequency, 

 the form a is more common than that of /3 ; and the forms a and /3 are more common 

 than that of 7, which is very rare." 



