I 9 --] Miller: Variations in Teredo navalis in San Francisco Bay 297 



By our system of planting and removing test timbers at regular 

 intervals in infected localities, it has been possible to get a limited 

 number of shells whose age can be estimated with a considerable 

 degree of accuracy. These timbers, having been planted during 

 the height of the breeding season, when the water was swarming 

 with larvae, may safely be assumed to have been attacked within a 

 few days after planting. As the seasonal period of attachment of 

 larvae continues during several months, specimens of varying ages 

 will of course be found in the same timber; accordingly, the larger 

 specimens were selected in each case, as representing those which 

 were first to enter the wood after it was placed in the water. - 



TABLE 1 

 Rate of Growth of Ridges on Shells of Teredo at Goat Island 



Age 



Number of ridges: 



