••'> 

 '*■'-& 



Fig. 3. A. Detail of vertical face of limestone ledge of the intertidal 

 zone, with, rich gasteropod fauna. Several hundred individuals to the square 

 foot may often be counted on such a surface. Bic. Gulf of St. Lawrence. 

 L. D. Burling, photographer. 



B. Detail of beach shown in A pi. 1. figure shows average abundance of 

 gasteropod life on the stony type of intertidal zone. H. I. Smith, photog- 

 rapher. 



