2? PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 125 
system, which features a narrow entrance (Golden Gate), two long 
narrow divisions extending northward and southward from the middle 
section, and the combined discharge into the northern arm of two 
major rivers—the Sacramento and San Joaquin. In addition to 
mechanical effects, the complex interaction of the inflow of these and 
lesser rivers and streams with the diurnal ebbing and flooding tides 
through the Golden Gate results in significant fluctuations, especially 
in salinity and temperature. 
Salinities at the localities for this species range from polyhaline to 
oligohaline. At Fort Point, at the Golden Gate entrance to San 
Francisco Bay and less than a mile seaward from Station 83 (Crissy 
Field Buoy), salinities average 30-31 °/o0. From there, average salin- 
ities decrease progressively inland to about 27-29 °/o.. in the middle 
southern division and to about 25 °/oo at the southern end of San Pablo 
Bay, to 15-16 °/oo at Crockett at the seaward end of Carquinez 
Straits, to 10 °/oo at Martinez at the other end of the straits, to 1 °/oo 
at Pittsburg, and to 0.3 °/oo at Antioch (Miller, et al., 1928; Filice, 1954). 
As to temperature, the study of Miller, et al. (1928), conducted in 
July 1923, indicates that the lowest average surface temperatures are 
found at the entrance to the bay (14.1°C at Fort Point) with increases 
to 17.8°C at Oakland in the middle bay, to 20.6°C at Dumbarton 
Bridge in the southern part, and to 19.1°C at Crockett in the north- 
ern arm. 
As to other factors, turbidity is relatively high at the two ends of 
the bay system, especially at the northern end owing to silt from the 
rivers. Toward the mouth of the bay, the water becomes clearer with 
turbidity normally negligible at the Golden Gate. As might be ex- 
pected, oxygen content is higher in the colder, less polluted water at 
the bay entrance. In the upper bay, it is almost invariably below the 
saturation point (Filice, 1954). Filice could find no evidence, however, 
that there was a correlation between depressed oxygen values and the 
presence of wastes, or that the amounts of oxygen present affect the 
bottom fauna in any way. 
Judging from environmental conditions at the various collection 
sites in San Francisco Bay, I conclude that Synidotea laticauda is able 
to tolerate a wide range of salinities, temperature fluctuations, turbid- 
ity, and other estuarine conditions. I will present evidence in a forth- 
coming paper (with R. J. Menzies) that it probably is a relict of a 
warm water species that occurred in the bay region in earlier times 
when warm waters extended far northward along the Pacific coast. 
Synidotea species 
Locauiry.—California: San Francisco Bar Channel (Station 90). 
REMARKS.—One specimen too badly damaged for positive specific 
identification was taken from the buoy chain at a depth of 14.8 meters. 
