138. Tlif purple sea urchin, Strongylocen- 

 trottis ]>tirj)uratus, has almost the same 

 range as its larger relative in Plate 137, hut 

 is seldom more than 3 inches across and oc- 

 curs in great heds, especially in surf-swept 

 meas. In soft rock each urchin sits in its own 

 pothole. (California. \\'ood\' \\'illiams) 



139. A close-up ot the mouth of a sea urchin 

 reveals the five white teeth that grind the 

 seaweeds and animals on which it feeds. 

 (West Indies. Fritz Goro: Life Magazine) 



