ECHINOIDEA. 29 



A. ENBOBRANCE1ATA. 



Entobranchiata, Bell, P. Z. S. 1881, p. 417. 



Abranchiata, Ludwig, Zeitschr.f. wiss. Zool. xxxiv. (1880) p. 82. 



The Endobranchiata are regular Euechinoidea in which there are 

 no external gills or peristomial slits ; the oral membrane is covered 

 with several sets of both radial and iuterradial plates ; the peri- 

 gnathic arches are interradial and incomplete. 



Family 1. CIDARID^l. 



Cidaridse, Gray, Ann. Phil. xxvi. (1825) p. 426; Wyv. Thorns. Phil. 



Tr. vol. 104 (1874) p. 721 ; Zittel, Hdb. Palaont. i. (1879) p. 493 ; 



Duncan, J. Linn. Soc. xxiii. (1889) p. 26 ; Doderlein, Japan. Seeigel. 



(1887) p. 3. 

 Cidaride'es au[n]grististellees, Gras, Ours. foss. de VIsere, (1848) p. 20. 

 Angustistellees, Desor, Syn. Ech.foss. (1858) p. 2 [2 bis]. 

 Goniocidarida, Raeckel, Gen. Morph. (1866) p. lxxiii. 



The Cidaridse are endobranchiate Euechinoidea in which there 

 are no spheridia ; the calyciual area is extensive ; organs of Stewart 

 appear to be always developed ; the plates of the ambulacral area 

 remain separate from one another and are all primary. The spines 

 are strong aud often long, and are frequently of bizarre shapes ; iu 

 structure they are acanthodictyote and acanthostracous throughout 

 their whole extent from the ring upwards ; the central axial portion 

 exhibits a simple fenestrated structure ; the spicules in the walls of 

 the ovary are triangular or triradiate in form. 



One genus : Cidaris. 



B. ECTOBRANCHIATA. 



Ectobranchiata, Bell, P. Z. S. 1881, p. 417. 



Branchiata, Ludwig, Zeitschr.f. iviss. Zool. xxxiv. (1880) p. 82. 



The Ectobranchiata are regular Euechinoidea in which external 

 gills are always developed and the edges of the peristome indented 

 by five pairs of notches ; the oral membrane is covered with radial 

 plates only, and these may be numerous or reduced to five pairs ; 

 the perignathic arches are radial and complete. 



Family 2. ECHINOTHURIIDyE. 



Echiiiuthuridee, Wyv. Thorns. Depths of the Sea (1873) p. 164 ; id. 



Phil, Trans. 164. (1874) p. 730; A. Ag. Chall, Rep. (1881) p. 71; 



Ludxviq, Zeitschr.f. w. Zool. xxxiv. (1880) p. 82; Sarasin, Ergebn. 



Ceylon, i. 3 (1888) p. 129. 

 Diadematoida Streptosomata, Duncan, J. Linn. Soc. xxiii. (1889) 



p. 40. 



The Echinothuriidae are regular ectobranchiate Euechinoidea, in 

 which the organs of Stewart are more or less retained ; they may 



