ASTEK1O1DS. 



503 



known as Heart-Urchins. The Genera Spatangus, Bris- 

 S2is, Amphidotus, and others belong here. Most of the 

 Spatangidae bury themselves in mud or sand. Brissus 

 is found on the coast of Florida. 



SUB-SECTION III. 



THE ORDER OF ASTERIOIDS, OR STAR-FISHES. 



THIS Order comprises echinoderms which are more or 

 less star-shaped, the disk or central portion gradually 

 merging into the rays, beneath which the locomotive 

 suckers extend the whole length ; and the calcareous 

 skeleton is composed of movable pieces, so that these ani- 

 mals can bend themselves in any direction. There is al- 



Fig. 488. 



Star-Fish, A steracanthion. Coast of New England. 



most every possible form, from those which have the arms 

 long and graceful to those in which the arms and body 



