EXPLANATION OF PLATE 3. 



Fig. 1. Lower (left) valve of Ostrea cuciilata; (Born) d, dorsal edge, v, ventral ditto,"ff, 

 anterior margin, ^5, posterior ditto, showing a large blister with the opening of 

 worm tube on the anterior margin. 



„ 2, Upper (right) valve exhibiting two blisters ; the one with a dotted outline near the 

 ventral edge, is covered by a calcified layer : the other is on the membranous 

 stage. 



„ 3. Upper valve showing a larger blister, the work of a single worm (right hand figure). 

 The same with the surface of the blister removed showing the position occupied 

 by the worm (left hand figure). 



