1918 | Packard: Molluscan Fauna from San Francisco Bay 225 
sibly they are due in part to the effects of hydraulic mining, which, 
according to Davidson, resulted in the deposition of 60 feet of mud 
within San Francisco Bay. Dall in a personal communeation states 
that ‘‘the changes (diminution) of the fauna (molluscan) since my 
first dredgings in 1865 are notorious among local collectors.”’ 
The dredging of pholadid specimens at unusual depths within the 
Golden Gate leads to a special investigation with the view of deter- 
mining the bathymetric range of these forms. Dredge hauls were 
made with the oyster dredge at stations D 5845 and D 5846 within 
the outer portion of the Golden Gate. A number of boulders repre- 
senting a variety of rock types were obtained. The rocks that had 
been bored by mollusks were measured, weighed, and then broken in 
order to obtain the enclosed mollusks. Rocks number 1 and 7 were 
serpentine, number 16 being a gray schist. The remainder of the 
rocks that had been bored were sandstone or shale, presumably of 
Franciscan Jurassic age, such as occur along the shores of the Golden 
Gate. 
Within old pholadid borings were found a number of molluscan 
species, several of which are not commonly considered as nestlers, 
These included Zirfaca gabbi, Macoma inquinata, Ostrea lurida, and 
Hinnites giganteus. The last species was found in a large pholadid 
boring, in which it had become imprisoned and to which it had at- 
tempted to conform but eventually had been killed by its restricted 
quarters. 
The fauna from the different rocks is given in the accompanying 
table (4), together with the rough dimensions and weights of each 
boulder. 
Living pholads were obtained in rocks number 6 and 10 at a depth 
of 59 fathoms. The boulders from which these specimens were taken 
are too large and too irregular to have been moved from shallower 
water during the life of the mollusk. This occurrence indicates a 
bathymetric range for these borers considerably greater than is gen- 
erally attributed to them, especially by geologists who commonly 
employ them as indicators of ancient strand lines. Even these figures 
do not represent the maximum range for members of the family, since 
Dall informs the writer that a specimen has been taken from a depth 
of 1270 fathoms. 
