ECHINODERMATA. 25 



Genus— CLDARIS, Klein. 1734. 



Echinus, Linneevs, Ilissenger, &c. 



Echinites or Histrix, Bourguet. 



Cidakis, Klein, Leshe, De/rance, Blainville, Ayassiz, Desor. 



Cidarites, Lamarck, Goldfuss, Gray, Desmoulins. 



General form circular or turban -shaped ; test thick, sub-spheroidal, nearly equally 

 flattened on the under and upper surfaces. 



Ambulacral areas very narrow and undulated, supporting only minute granuloid 

 tubercles, or small granules, disposed in two, four, or six close-set rows. 



Inter-ambulacral areas at least four times the width of the ambulacral, furnished with 

 two rows of large primary tubercles, from four to six in a row, — rarely there are ten. 



The tubercles are perforated ; the bosses are large and prominent, and their summits 

 are smooth or crenulated ; the areolas are wide, and in general are deeply excavated ; 

 they have a round or oval figure, and their elevated margin is in general surrounded by a 

 complete circle of granules (the scrobicular circle). 



The miliary zones are concave, and more or less wide in proportion to the size of the 

 primary tubercles ; they are filled with numerous rows of small, close-set granules. 



The poriferous zones are narrow ; the pores are unigeminal and contiguous ; they are 

 separated by septa more or less thick. 



The spines are robust and massive, cylindrical, fusiform, or claviform ; their surface is 

 covered with longitudinal lines, or furnished with prickles, granules, or other asperities, 

 which often assume a linear arrangement. 



The mouth opening is circular or pentagonal, without notches ; the buccal membrane 

 is covered with imbricated scales, on which the pores- from the zones are prolonged. 



The apical disc is large, and is composed of pentagonal, nearly equal-sized, genital 

 plates, and triangular ocular plates. 



The lantern is powerful, composed of massive pyramids, the branches of which are not 

 united at their summits ; the teeth are canaliculated, and formed of a folded plait, without 

 a carina on the inner surface. 



Notwithstanding the limitation of the genus Cidaris of Klein., by Lamarck, Goldfuss, 

 Agassiz, and Desor, it still forms an extensive group of Urchins, which range from the 

 Palaeozoic rocks into our modern seas. 



This genus divides itself into two types ; in the one, the mammillary bosses have 

 smooth summits ; in the other, they are more or less crenulated. 



The first type. — Tubercles with smooth and uncrenulated bosses, exist in our present 

 seas, and are found fossil in the Carboniferous, Triassic, Cretaceous, and Tertiary rocks. 



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