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GENUS II. Cidaris. With a spheroidal or depressed 

 orbicular crustaceous or testaceous internal solid skin, fur- 

 nished with tubercles perforated through their summits, 

 supporting moveable spines, the largest of which ai'e bac- 

 ciliform. The ambulacra are complete, reaching from the 

 vertex to the mouth, and bordered by two multiporous 

 bands. The mouth beneath, central, and supplied with 

 teeth. The vent above, vertical. 



In the species of this genus, the tubercles are pierced 

 through their apex, for the passage, it is presumed, of a 

 muscular thread ; the ambulacra are narrower and more 

 regular than in those in which the tubercles are imperforate ; 

 and the little porous bands which border the ambulacra are 

 less diverging and more nearly approximated. Their spines 

 are various, never uniformly setous, but either large and 

 sudiform and as if truncated, or long and crenulated, with 

 others very small and numerous, surrounding, as with a 

 little collar, the base of the larger ones. In some of the 

 species of this family, the margins round the papillous 

 tubercles are regularly crenulated. Lamarck divides these 

 echini with perforated spines into turbans and diadems. By 

 the former term he designates those which are rather 

 elevated, but nearly spheroidal, with the ambulacra winding ; 

 by the latter he means those which have a round depressed 

 shell, with straight ambulacra, and with spines generally 

 hollow. 



Sp. 1. Cid. imperialis. Subglobose, depressed on both 

 sides ; the ambulacra and smaller spines of a violet colour ; 

 the larger spines cylindrical, but rather ventricose, striated 

 in their apex, and marked with white rings. 



Cid. papillata major. Leske ap. Klein, Tab. vii. fig. A. 



This cidaris differs from cidaris mammillata, Kl. in 

 its shell being more globular, and in its tubercles being 

 pierced. 



2. C. diadema. Nearly circular : the vertex depressed ; 



