EXPLANATION OF PLATE V. 



Fig. 1. Lower (left) valve of Ostrea ciiculaAa ; (Born) d, dorsal edge, 

 V, ventral ditto, a, anterior margin, p, posterior ditto, showing 

 a large blister with the opening of the 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 in 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). 



