2!):5 



The burrows of Bankia setacea differ from those of the two species of Teredo 

 found in San Francisco Bay in two important particuhirs. They are larger, and they 

 present continuous minor deviations froni the main axis of tiu- hurrow, so that the 

 burrows of Bankia are less symmetrical and regular than those of Teredo (compare 

 figures 22 and 89). The slight ridges which occur on the walls of the burrow of Bankia 



Fig. 116. Pile from Seattle, driven December, 1922, pulled June, 1924. Entirely destroyed at mud line 

 by Bankia setacea. 



(1) Split section, mud line to 1 ft. above. 



(2) Section 1 ft. to 3 ft. above mud line, with bark removed. 



are due to abrupt Init slight changes in the direction of boring, resulting from a shift 

 in position of the foot and shell. They are sometimes less than a millimeter apart. 

 The burrow of Bankia enters the pile at right angles to the surface as a small 

 pinhole, and turns obliquely, usually downward, enlarging rapidly within 2 inches of 

 the surface to I4 inch in diameter, and within 4 inches to a diameter of 3 g to J 2 inch. 

 The largest burrows we have found in San Francisco Bay were '^ 5 inch in diameter 

 at the widest portion, and exceeded 30 inches in length. 



