ECHINOIDEA. 29 
A. ENDOBRANCHIATA. 
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 interradial plates; the peri- 
gnathic arches are interradial and incomplete. 
Family 1. CIDARID. 
Cidaride, Gray, Ann. Phil. xxvi. (1825) p. 426; Wyv. Thoms. Phil. 
Tr. vol. 164 (1874) p. 721; Zittel, Hdb. Paldont. i. (1879) p. 493; 
Duncan, J. Linn. Soc. xxiii. (1889) p. 26; Déderlein, Japan. Seeigel. 
(1887) p. 3. 
Cidaridées au[{n]gustistellées, Gras, Ours. foss. de l’ Isere, (1848) p. 20. 
Angustistellées, Desor, Syn. Ech. foss, (1858) p. 2 [2 bis]. 
Goniocidarida, Haeckel, Gen. Morph. (1866) p. lxxiii. 
The Cidaride are endobranchiate Euechinoidea in which there 
are no spheridia ; the calycinal 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 and often long, and are frequently of bizarre shapes ; in 
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, Zettschr. f. wiss. 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. ECHINOTHURIIDA. 
Kehinothuride, Wyv. Thoms. Depths of the Sea (1873) p. 164; zd. 
Phil. Trans. 164. (1874) p. 780; A. Ag. Chall. Rep. (1881) p. 71; 
Ludwig, Zeitschr. f. w, Zool. xxxiy. (1880) p. 82; Sarasin, Ergebn. 
Ceylon, i. 3 (1888) p. 129. 
Diadematoida Streptosomata, Duncan, J. Linn. Soc. xxiii. (1889) 
p. 40. 
The Echinothuriide are regular ectobranchiate Euechinoidea, in 
which the organs of Stewart are more or less retained; they may 
