62 ECHINODERMATA. 



ECHINODERMATA. 



Animals having a radiate structure, covered with 

 a more or less leathery coat, in which are imbedded 

 variously - shaped calcareous pieces, sometimes 

 minute and few, sometimes so numerous as to form 

 a shelly box, composed of plates moveable or tightly 

 bound together, and increasing by the deposition 

 of particles around the margin of each individual 

 plate. The radiation is characterised by the 

 number five. 



With a bag-like stomach, furnished with 

 only one aperture ; the body lobed, or ex- 

 panding into rays Hypostomata. 



With a distinct digestive canal, furnished 

 with a mouth and vent : outline- of body 

 entire Ditremata. 



Sub-Class I. Hypostomata. 



Digestive canal unsymmetrical ; calca- 

 reous shell composed of moveable pieces, 

 forming an external skeleton Crinoidea. 



Digestive canal symmetrical ; calcareous 

 shell, composed of moveable pieces, forming 

 an internal skeleton, with a covering some- 

 times leathery, and sometimes calcareous . Asteroidea. 



Order I. CRINOIDEA. 



Comatula (Lamk.). Body with 5 forked pinnate 

 rays. When young, seated on a long simple jointed 

 attached stem. When adult, free, stemless, with 



