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GOIDE TO LOCALITIES. 



shores, Purpura lapillus, of which the variations in color and 

 form have been noted above. The varieties are nowhere so 

 abundant as at Nahant, where brilliantly colored and variegated 

 individuals are not uncommon. The three species of Littorina 



Sea urchins in excavations. 

 (After Few kes, hy courtesy of the Essex Institute.) 



with their numerous varieties also are abundant. L. jwlliata and 

 L.rudis are common on the seaweed and rocks near low water, 

 while L. littorea may be met everywhere. The only pelecypods 



