170 POPULAR HISTORY OF THE AQUAIIIUM. 



Cidaris papillata has only one long spine on each inter- 

 ambulacral plate, and these are long and straight. A Cidaris, 

 with all its spines perfect and radiating from the central 

 depressed globe, is a very beautiful object. 



Star-fisJies, their Classification, 



1. The Crinoidce, qx pinnigrade Stars, have arms capable 

 of independent motion, assisted by cirrhi which spring from 

 membranes attached to the arms. — Feather -stars. 



2. The Op)limrid(B, or spinigrade Stars, have no mem- 

 branes on the arms. They have cirrhi, but the motion is 

 effected by means of spines on the movable arms. — Brittle- 

 stars. 



3. The AsteriadiE, or cirrhigrade Stars, have no true or 

 independent arms, but their bodies are lobed, or fingered, 

 and the lobes are channeled underneath, with rows of cirrhi 

 or suckers in the channels, which are the organs of motion. 

 — CrosS'fisli. 



One specimen of each must suffice. They are not sub- 

 jects suitable to heep in Aquaria, as they do not live happily 

 in confinement, but soon kill themselves, or otherwise die. 



