224 



LECTURE X. 



cular system distinct from the chylaqueous and digestive systems ; 

 the latter in a distinct abdominal cavity ; in some a distinct respi- 

 ratory organ. 



Order Crinoidea. 



Body with ramified rays, supported temporarily or permanently on 

 a jointed calcareous stem. Alimentary canal with mouth and vent. 

 Sexual organs very numerous and distinct. 



Family Encrinidx. Body persistent on stem. 



Genera Enci-inus, Petitacrinus (most of the 

 species are extinct). 

 ComatulidjE. Body liberated from stem in the adults. 

 Genera Comatula. 



Order Asteroidea (Star-fishes). 



Body radiate ; integument hardened by calcareous pieces, and 

 more or less armed with spines. No dental apparatus. Alimentary 

 canal symmetrical, and in some without a vent. 



Family Ophiuridx. Genera, Astrophyton, Ophiunyx, Ophio- 



thryx, Ophiomastyxt Ophiocoma, Ophio- 

 lepis, Ophioderma. 

 Genera, Luidia, AstrQpecten, Ctenodiscus, 

 Archaster, Stellaster, Astrogonium, Ore' 

 aster, Pteraster, Asteriscus, Culcita, 

 Ophidiaster, Choetaster, Solaster, Ecliin- 

 aster, Asteracanthion. 



Stelleridm. 



Order Cystoidea. 



Body spheroid, incased in a crust of infiexibly joined calcareous 

 pieces ; and supported on a jointed stem. 

 (All the species are extinct.) 



Order Echinoidea (Urchins). 



Body spheroid or discoid, incased in a crust of inflexibly joined 

 calcareous plates, and armed with spines. Dental system complex, 

 forming a part called 'lantern.' Intestine convoluted, with a distinct 

 vent. 



Family Clypeasteridm. Genera Clypeaster, Scutella, Encope, 



Botula, Lohophora, Echinocyamiis, 

 Mellita, Echinanthus. 

 EcHiNiDM. Genera Echinus, Cidaris. 



Spatangidm. Genus Spatangus. 



