192 UPPER, OR FLINTY CHALK. 



sequently to the mineralization of the latter. One specimen in my col- 

 lection is particularly interesting ; the shell, as usual, is converted into 

 spathose calcareous spar, and about one-fourth of its cavity is occupied by 

 pure black flint, the surface of which, together with the sides of the shell, 

 are incrusted with rhombic crystals of carbonate of Hme*. 



Locahties. Upper chalk, throughout Sussex. 



Spatangus. Body cordiform, or ovate ; vent lateral. 



40. Spatangus cor anguinum. Org. Rem. Vol. iii, PL S, figs. 11, 12. 

 Cordiform, narrow extremity truncated, surface granulated; back 



convex, with five grooved quadriporous ambulacra, the two shorter ones 

 extending obHquely towards the truncated extremity, and having a ridge 

 between them, which passes to the vent ; the two longer ones incHned 

 towards the broader end ; the fifth extending direct to the mouth, and 

 forming a deep groove along the back. Mouth transversely reniform, its 

 lower margin but slightly produced ; vent placed in the upper pait of the 

 truncated extremity. 



This species is too well known to require farther observation. 



Localities. Abundant in the upper chalk throughout Sussex. 



41. Spatangus rostratus. Tab. xvii. figs. 10. 17. 



Cordiform, dorsal ridge rostrated ; anterior part of the shell depressed. 



This species resembles the preceding, but the ridge which extends 

 from the vertex to the vent is strongly produced, while the opposite side 

 of the shell is considerably depressed ; these characters are so constant, 

 that I have ventured to assume them as specific distinctions. 



Localities. Chalk-pits, near Brighton. 



42. Spatangus jo/am<6r. Tab. xvii. figs. 9. 21. 



Ovate, vertex rather depressed ; surface nearly smooth, with eight ( ?) 

 biporous ambulacra, diverging in pairs on each side the back and front ; 

 dorsal groove superficial, smooth, extending to the mouth ; base slightly 

 convex ; mouth transversely reniform ; vent placed in the upper part of 

 the side. 



* Scilla (Tab. xix. fig. 3,) gives the representation of an echino-cidaris, partially filled 

 with crystals " ripieni d'ingemamento bellissimo." 



