EXPLANATION OP PLATES 

 PLATE 19 



Fig. 1. Siphonal end of Teredo navalis, showing position of pallets. X 5. 



Fig. 2. Pallets in position, closing entrance to burrow. The dark area at 

 the right is the opening to the burrow of an older, retracted specimen. X 10. 



Fig. 3. Pallets arranged in pairs, illustrating variation in two members of 

 the same pair. X 5. 



Fig. 4. Series of pallets from the Oakland Harbor Light Station, represent- 

 ing ages of approximately two weeks (?), one month, two months, three months, 

 and four months, respectively. 



Fig. 5. Comparison of a normal and nearly typical pallet from Goat Island 

 with an older one from the same location, showing maximal effect of age and 

 erosion. 



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