Plate II. Set of I'.ioi), Gret'invicli Bay. Upper two rows 

 sliow average size in Sp]>teml)er. Average on Septemljer lUtli, 

 25mm. Average on September 24tli, 21). 5mm. The two shells in the 

 lower vow at the right were kept in the car horn September 10th to 

 Octol)er 13tli. Third row, average size for Octol)er under natural 

 conditions, 34.56mm. Fourth row. Shells kept in car on house- 

 boat from Septemljer lOtli to Octol)er IGtli. 



