DIADEMADtE. • 107 



"Diadems;" these Dr. Gray* afterwards converted into two genera, separating from 

 the Diadems Cidaris radiata, Leske,t as the type of his new genus Astropyga. The 

 genus Cidarites of Lamarck was considered as a natural family, composed of the genera 

 Cidaris, Diadema, and Astropyga, which he thus characterised : 



Family 1. CiDARioiE. Cidarites, Lamarck. 



Body with two-sized spines; larger ones club-shaped, or very long; 

 spine-bearing tubercles perforated at the apex. 



Genus 1 . Cidaris, Klein, Lamarck ; Turbans. 



Body depressed, spheroidal, ; ambulacra waved; small spines compressed, 



two edged, two roioed, covering the ambulacra, and surrounding the base 



of the larger spines. 

 This genus may be divided according to the form of the larger spines ; 



the extra-ambulacral beads have only two rows of spines. 

 Cidaris imperialis, Lamk., Klein, t. 7, fig. a. 



Genus 3. Diadema. Diadems. 



Body orbicular, rather depressed; ambulacra straight, spines often 



fistulous. 

 Echinometra setosa, Rumph., Leske, Klein, t. 37, figs. 1, 2. 

 Echinus diadema, Linn., Syst. Nat., by Turton, vol. iv, p. 139. 

 Echinus calamaria, Pallas, Spicil. Zool., t. 2, figs. 4 — 8. 



Genus 3. Astropyga. 



Body orbicular, very depressed ; ambulacra straight; ovarian scales very 



long, lanceolate ; beads icith several series of spines. 

 Cidaris radiata, Leske, Klein, t. 44, fig. 1. 



The very meager characteristics by which this author has defined the last two genera 

 only show that a difference exists, but his description is insufficient for a correct diagnosis 

 between them ; hence various opinions exist regarding the characters and limits of the 

 genus Diadema ; and only one of the species enumerated as types, the Diadema setosa, 

 Rumph., is admitted to be a true Diadem. The valuable memoir of Herr W. Petersj 

 has removed some of the difficulties that surrounded this subject, and his grouping of the 

 living Diadems makes an important step towards a natural classification of one section of 



* 'Annals of Philosophy,' new series, vol. x, p. 42G, 1825. "An attempt to divide the Echinidae or 

 Sea Eggs into Natural Families." 



t Leske apud Klein, 'Naturalis Dispositio Echinoderniatum,' t. 44, fig. 1, p. IIC. 



X Uber die Gruppe der Diademen, ' Gelesen in der Konigl. Akademie der Wissensehaften,' Berlin, 

 Aug. 1853. 



