ASTEBOIDEA. 21 



ginal plates along the ray ; the marginals and adambulacrals do not 

 correspond in number or length. 



Four genera : Leptopty chaster, Astropecten, Psilaster, BatJiy- 

 biaster. 



Subfamily 2. LUIDIIN^E. 

 Luidiinae, Sladen, Chall. Rep. Ast. (1889) p. xxxi. 



Astropectinidaa in which the inferomarginal are separated from 

 the adambulacral plates by a small intermediate plate throughout 

 the ray. Marginals and ambulacrals corresponding in number and 

 length. 



One genus : Luidia. 



Family 4. PENTAGONASTERID^E. 



Pentagonasteridse, Perrier, Arch. Mus. vi. (1884) p. 231 ; Sladen, 

 Chall. Rep. Ast. (1889) p. xxxi. 



Phanerozonia in which the marginal plates are very large and the 

 diameter of the disk long in proportion to the arms. The skeletal, 

 as well as the marginal, plates may be naked or covered with 

 granules, are set close, and are rounded, polygonal, or stellate in 

 form. 



Two subfamilies. 



Subfamily 1. PENTAGONASTERIXJE. 



Pentagonasterinse, Sladen, Chall. Rep. Ast. (1889) p. xxxi. 



Pentagonasterida? in which the abactinal area is covered with 

 rounded, polygonal, or paxilliform plates. 



Two (or three) genera: Pentagonaster, Nyrnpliaster, ? Hippas- 

 terias. 



Subfamily 2. HIMASTERIK^. 



Mimasterinae, Sladen, Chall. Rep. Ast. (1889) pp. xxxii & 264. 



" Abactinal area with small stellate plates bearing true paxillae. 

 Actinal intermediate areas with imbricating plates in transverse 

 series, bearing paxilliform groups of spines." (Sladen.) 



One genus : Mimaster. 



Family 5. GYMNASTERIIDtE. 



Gymnasteriadse, Perrier, Nouv. Arch. Mus. vi. (1884) p. 229. 

 Gymnasteriidfe, Sladen, Chall. Rep. (1889) p. xxxiii. 



Phanerozonia in which the marginal plates are not all equally 

 developed. 

 Four genera : Porania, Cheilaster, Ehegaster, and Lasiaster. 



