UPPER, OR FLINTY CHALK. 193 



This species is a rare production of the chalk, and is distinguished by its 

 ovate form, and by the ambulacra not being grooved as in the two former 

 species. Its surface, in some instances, is covered vs^ith minute and in- 

 distinct papillae, but generally appears perfectly smooth; even the am_ 

 bulacra are scarcely perceptible. It is therefore possible, that a pair may 

 extend to the dorsal groove, although none can be detected in that situa- 

 tion, in the specimens in my possession. 



Figs. 9, 21, are different views of the same specimen. 



A spatangus nearly related to this species, has very recently been dis- 

 covered in the grey marl, at Hamsey ; the summit is depressed, the base 

 slightly concave, and the dorsal groove rather more distinct than in S. 

 planus. 



Locality. Lower chalk, near Lewes. 



43. Spatangus . Tab. xvii. figs. 22, 23. 



This species is perfectly smooth, and no traces of ambulacra are per- 

 ceptible. The mouth and vent are placed as in the preceding species, of 

 which, perhaps, the present specimen may be the shell in a young state. 



Mr. Konig informs me they are not unlike Spatangus prunella of La- 

 marck, except that the ambulacra are not visible. 



Figs. 22, 23, are sketches of the same individual. I have seen no 

 larger examples. 



Locahty. Brighton ; rather numerous in the Upper chalk. 



Ecf[iNiTAL Spines. 



It has already been mentioned, that these are the instruments of mo- 

 tion, and are fixed by ligaments to the tubercles, or papillae, of the crus- 

 taceous covering. 



Specimens in which they are still attached to the shell, are very rare 

 in a fossil state ; the only example that has been discovered in Sussex, is 

 in the possession of Miss Eebecca Godlee of Lewes ; it is a Cidaris papil- 

 lata, with four or five spines imbedded in the surrounding chalk. 



The spines generally present considerable variety both in their forms 



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