292 



Alaska, November 1, 1922, under the direction of the National Research Council 

 Committee, showed earh- stages of attack by B. setacea on January 2, following. 



The supposition that low temperatures are favorable to this organism is supported 

 by the fact that it occurs most commonly in deep water, and in San Francisco Bay 

 attains maximal size in the regions of Sausalito, Tiburon, and the San Francisco 

 waterfront. The relative scarcity of this form in localities south of San Francisco Bay 

 indicates that it does not thrive in the warmer waters of the southern California coast. 



In addition to temperature and depth, the local distribution of this species is 

 limited by minimal salinity requirements and, to a much less extent, by sewage 

 contamination. 



Bankia setacea is much less resistant to low and fluctuating salinities than is 

 Teredo iravalis. This difference may be in part physiological, and in part due to the fact 

 that the jointed, feather-like pallets of Bankia possibly afford a less effective mechan- 

 ism than the simple pallets of Teredo for sealing the entrance to the burrow against 

 the ingress of water of too low salinity. In any case, B. setacea is limited in its distribu- 

 tion in San Francisco Bay to regions where the average salinity is not much less than 

 25 parts per 1000, and the minimal salinity for the year probably not below 10 parts 

 per 1000. 



In this in\'estigation Bankia has not been found at all in San Pablo Bay, the 

 farthest point up-bay at which actual specimens have been obtained being Point 

 Richmond, although it is possible that the organism occurs in deep water as far as 

 Point San Pablo. There is one record of its occurrence for a time clear at the upper 

 end of San Pablo Bay, at Crockett, where it was reported by Mr. A. A. Brown, as 

 occurring in 1917-1918, in green piling that had lain awhile in the boom at Islais 

 Creek, after which it was driven at Crockett in the period from January to June, 1917. 

 Some burrows were detected in these piles at the time of driving, and the probable 

 interpretation of the data is that the piles were infected with Bankia while in the boom 

 in the lower bay, and that some of the organisms survived for a time in the new 

 locality. A careful search here and elsewhere in the upper bay since 1919 has not 

 brought to light any specimens of Bankia, and it does not appear probable that the 

 organism will be able to establish itself as a serious pest in San Pablo Bay unless the 

 salinity conditions prevailing there should become considerably and permanently 

 altered. 



The salinity requirements of Bankia setacea appear to be quite similar to those 

 of Limnoria, and the localities occupied by these two organisms in San Francisco Bay 

 are very nearly co-extensive, although Limnoria, being a hardier and more adaptable 

 organism, will sometimes successfully invade areas where Bankia is unable to become 

 established. 



As regards the effect of sewage contamination, Bankia, like Teredo, does not appear 

 to be deleteriously affected except in limited areas close to the mouths of sewers. 

 Thus at the foot of Channel Street in San Francisco, where a large sewer opens at the 

 head of a narrow channel, in which the sewage flows confined for several hundred 

 yards before reaching the bay, Bankia occurs at least a hundred yards up the channel, 

 where on a low tide the pH value was found to be 7.5 (.35 lower than the average 

 for this portion of the bay), and the bottom oxygen 4.38 c.c. per liter, or .86 less than 

 the average at the Ferry Building (see page 266). At this locality, in fact, Bankia 

 seriously damaged untreated piling in a temporary structure between February and 

 August, 1922 (see p. 237). Any ordinary degree of sewage contamination cannot 

 therefore be regarded as an effective deterrent to Bankia or other borers. 



