FOSSIL ASTEROIDEA 



475 



remarkable family, chiefly on account of the smallness of the 

 disc and of the extraordinary length of the arms. The arms 

 have what we must consider to have been the primitive arrange- 

 ment, since there is no lateral adhesion between them, and inter- 



Fig. 205. Aboral view of Odinia. x|. (After Perrier.) 



brachial septa are consequently entirely absent. The reduction 

 of the skeleton is a very marked peculiarity and, like the ten- 

 dency to the reduction of the skeleton of deep-sea fish, may 

 stand in some relation to the great pressure under which the 

 animals live. 



Fossil Asteroidea. 



The Asteroidea occur somewhat plentifully as fossils. In the 

 Lower Jurassic Asterias, Astropecten, Zuidia, Solaster, and Goni- 

 aster have already made their appearance. In the Cretaceous 



