PLATE VI. 



Fig. 12. Oyster growing on glass, viewed from the right side, showing 

 p, Left and right valves of prodissoconch ; Is, 2s, Limits of first and sec- 

 ond silphologic stages. 



Fig. 13. Same specimen as fig. 12, viewed from the left side through 

 the glass to which it was attached, p, Left valve of prodissoconch ; Is, 2s, 

 Limits of first and secoud silphologic stages; I, Margin of left valve be- 

 yond which the right (upper) valve extends. Figs 12 and 13 magnified 

 eighteen times. 



Fig. 14. Oyster growing on glass, viewed from right side, p, Left and 

 right valves of prodissoconch; Is, 2s, 3s, 4s, Limits of first, second, third 

 and fourth silphologic stages of right valve. Magnified six times. 

 (554) 



