^ 71. THE ECHDfODEEMATA. 75 



FaHILT : AsiEBOrDAE. 



Genera: Luidia, Astropecten, Ctenodiscus, Archaster, SicUaster. Astrogo- 

 nium, Oreaster, Pteraster, Asteriscus, Cvlcita, Ophidiaster, Chaetasier, 

 Solaster, £chi/iaster, Astercucanihdoiu 



ORDER m. ECHiyOWEA. 



The calcareous shell forms a sfiherical or discoid shield, composed of im- 

 K arable plates. The digestive canal is asymmetrical. 



Fa3iIILT: ECHTNIDAE. 



Ger.-ra : Echinus, Cidaris. 



FA3iTLT ; ClYPEASTEIDAi;. 



G^xera : lagaTmm, Scuteila, Enmpe, Rotula, LabopkorcL, EddnocyamuSy 



MeUita, Ediinantkus. 



Familt : Spataxgidab. 

 Genus: Spatangus. 



ORDER IV. HOLOTBZ'RIOIDEA. 



In place of a calcareous shell, the cutaneous envelope contains a greater 

 or less number of calcareous reticulated corpuscles. The oesophagus is 

 surrounded by a calcareous ring, c-onstitutiag the rudiment of an internal 

 skeleton. The body is cylindrical. The digestive canal, generally asym- 



metrieaL 



Family : Holotetukinae. 

 Grenera : Hdiathuria. Pentactsu BohadscMa, Cladolabes. 



Famtlx: SxxAPnxAE. 

 Genera : Synapta, Chirodota. 



ORDER V. SIPUyCULOIDEA. 



The cutaneous envelope is coriaceous, and free from calcareous corpus- 

 cles. There is no calcareous ring about the oesophagus. The body is 

 cylindrical ; the digestive canal, u«na11v ayy^aietrical. 



Family : Sip€XCLxidail 

 Genera : Sipttnadus, PhasoaLasama. 



Family : Echtteidae. 

 Genera : Thdassema^ Eddurus. 



