BOOK FOURTH. 
ECHINODERMATA. 
CLASSIFICATION. 
§ 71. 
Tae Ecuinoperms have a more or less coriaceous envelope, filled with cal- 
careous, reticulated corpuscles. These last are sometimes so numerous that 
they form a real shell, composed of plates, movable, or tightly bound 
together. In the ray-like; symmetrically-arranged gystems of organs, the 
quinquenary number prevails. 
In many species the digestive canal is asymmetrical. All are marine, 
and most of them move by means of particular, erectile suckers. Others 
progress by vermiform motions; and some swim freely by moving their rays 
like oars. Only a few are stationary. All are without copulatory organs. 
ORDER I. CRINOIDEA. 
The calcareous shell, composed of movable pieces, forms a true cutane- 
ous skeleton. The body is ray-like; the digestive canal, asymmetrical. 
Famity: Enorrnrpae. 
Genus: Pentacrinus. 
Famity: Comarvinan. 
Genus: Comatula. 
ORDER I. ASTEROIDEA., 
The calcareous shell, composed of movable pieces, forms an internal skel- 
eton. The cutaneous covering is sometimes coriaceous, and sometimes cal- 
careous, The body is ray-like, and the digestive canal symmetrical. 
Famity: Oparuripas. 
Genera Astrophyton, Ophionyx, Ophiothriz, Ophiomastiz, Ophiocoma, 
Ophiolepis, Ophioderma. 
