ECHINOIDEA. -7 



ossicles, so that the arms can be twisted round foreign objects or 

 rolled towards the mouth ; the ossicles not invested by definite 

 plates, but the covering-skin more or less granular. Arms simple 

 or branched, arm-spines represented by papillae. Bursal clefts may 

 open directly into ccelom, when true bursae are wanting. No true 

 teeth ; mouth-shields and oral spines present or absent. Madre- 

 porite present or absent, and when present as many as five may be 

 found. Pedicellaria-like processes sometimes present. Some at 

 least can swim. 

 Two subfamilies. 



Subfamily 1. ASTRONYCIN^E. 



Astronycinae, Ljungman, CEfv. Vet.-Ak. Forhlg. 1866 (1867) p. 334. 



The clefts at the sides of the arms open into bursas. The arms 

 undivided. Oral spines or papillae present, but no oral shields. 

 Madreporite single. 



One genus : Astronyx. 



Subfamily 2. GORGOffOCEPHALIN^E. 



Gorgonocephalinae, Ljungman, CEfv. Vet.-Ak. Forhlg. 1866 (1867) 

 p. 335. 



The clefts at the sides of the arms open directly into the ccelom. 

 The arms branch, often very considerably. Oral spines or papilla? 

 present, but no oral shields. Madreporite single or multiple. 



One genus : Gorgonocephalus. 



Division II. ZYGOPODA, 



Zygopoda, Bell, Ann. % Mag. viii. (1891) p. 214. 



The Zygopoda are Eleutherozoa in which the podia extend more 

 or less uninterruptedly from the calycinal to the oral region. 



Class XI. ECHINOIDEA. 



Echinus, Linn. Syst. Nat. x. (1758) p. 663. 



Echinides, Lamk. Syst. (1801) p. 345 ; de Bl.Dict. Sci. Nat. lx. (1830) 

 p. 178 ; id. Actinol. (1834) p. 1U7 ; Desmoulins, Act. Soc. Linn. Bor- 

 deaux, vii. (1835) p. 167. 



Oursins, Cuvier, Tab. Elem. (1798) p. 647. 



Echinoides (Echinoida), Latreille, Fam. Nat. (1825) p. 532. 



Echinida, Macleay, Hor. Entomol. 1819, p. 316 ; Gray, Ann. Phil x. 



(1825) p. 423 : id. Brit. Bad. (1848) p. 2. 

 ihinida?, Flem. Brit. An. (1828) pp. 473, 47^ 



Echinidte 



