Pftoio* '/y] 



TWO SEA-URCHINS. 



In both these forms the spines are comparatively few. They serve to give an ide 

 diversity of form there is in this family. In the upper figure, though the spines are few 

 an enemy at a safe distance. In the lower photo they are very stout. 





[//. /. Sfie/'.i/onf 



with the other illustrat 



ions, of the great 



they are long and so di 



sposed as lo keep 



