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 EncbinidjE. Body persistent on stem. 



Genera Encrinus, Pentacrinus (most of the 

 species are extinct). 

 CoMATULiDM. 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 Ofhivribje. Genera, Astrophyton^ Ophionyx, Ophio- 

 thryx, Ophiomastyx^ Ophiocoma, Ophio- 

 lepis, Ophioderma. 

 Stelleridm. Genera, Luidia, Astropecten, Cteiiodisciis, 

 Archaster, Stellaster, Astrogonium, Ore- 

 asteVf Pteraster, Asterisciis^ Culcita, 

 Ophidiaster, Chcetaster, Solastery Echin- 

 astevy Aster acanthion. 



Order Cystoidea. 



Body spheroid, incased in a crust of inflexibly 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 Clypeasterid^. Genera Clypeaster, Scutella, Ericope, 



Botula, Lobophora, Echinocyamus^ 

 Mellita, Echinanthus. 

 EcHiNiDM. Genera Echinus, Cidaris. 



Spatangidje. Genus Spatangus. 



