38 University of Calif orni-a Puhlications in Zoology [Vol.18 



Sumner (Sumner, et al., 1914, p. 55) gives the following comparison 

 of the mean annual temperature of San Francisco Bay with that of 

 the lower third of Chesapeake Bay, both bays being located in about 

 the same latitude : 



Mean Range 



San Francisco Bay 12.91° C 8.35° C 

 Chesapeake Bay 14.38° C 22.12° C 



Although it is possible that the species of shipworms found in 

 Chesapeake Bay may not be able to live in San Francisco Bay because 

 adapted to the particular conditions of the Chesapeake Bay, in the 

 absence of definite knowledge of the breeding habits of the species 

 found in San Francisco Bay we may assume that there is no very great 

 difference in the general breeding habits of these two species. If 

 there be any difference we may expect that in San Francisco Bay, 

 where the temperature must fall off the less rapidly in the latter part 

 of the year, the breeding season of the Pacific Coast species of ship- 

 worms may continue later than that of the Atlantic species, and that 

 egg-laying may possibly begin earlier in the spring in San Francisco 

 Bay than in Chesapeake Bay. The period of possible infection of tim- 

 ber on the Pacific Coast may therefore be longer than on the Atlantic ' 

 Coast. Thus, it is not improbable that even in normal years Teredo 

 larvae may be carried from the main portion of San Francisco Bay 

 into San Pablo Bay by the tides of the late summer, and that they 

 may acquire at least a temporary foothold in accessible submerged 

 timber. It should be born in mind, however, that the data for rate 

 of growth given by Sigerfoos are for shipworms living in that part of 

 Chesapeake Bay where the salinity is not greatly reduced, and that 

 these rates should therefore be compared with the rate of growth of 

 shipworms in the main part of San Francisco Bay rather than with 

 the supposed rate of grow^th of the shipworms found in San Pablo Bay. 

 The general conditions throughout a normal year at these localities 

 in the upper part of San Pablo Bay seem to include a period in which 

 the surface salinity, at least on certain tides, must be reduced to 

 practically zero and the bottom salinity to but a few points above zero. 

 Such a condition, which may be of annual recurrence in this vicinity, 

 appears to be sufficient to kill all shipworms which may have taken 

 ■ hold of marine timber in these localities. This condition of greatly 

 reduced salinity in the spring, moreover, probably obtains during an 

 average year during so great a portion of the year as to effectually 

 prevent the existence of shipworms long enough to do notable damage, 



