322 University of Cahforma Publications in Zoology ‘SVou.13 
Group 7. Sand and shells 
Living: Mya californica 
Macoma balthica 
Epitonium hindsi 
Dead: Mya california 
Paphia staminea 
Epitonium hindsi 
Nassa fossata 
Nassa perpinguis 
Thais lamellosa 
The above list shows several different associations of species. Of 
the prevalent species, Cardium corbis, Macoma nasuta, Mya arenaria, 
and Zirfaea gabbi appear to be predominantly mud-dwelling forms; 
while Mya californica, Macoma balthica, M. inquinata, Ostrea lurida, 
and Thais lamellosa may be classed as sand dwellers. Although these 
conclusions are tentative, because of the paucity of the hauls upon 
which they are based, they suggest the broad features of the different 
molluscan communities. 
RELATION TO SALINITY 
In order to determine the influence of salinity upon molluscan 
distribution, a comparison of a curve showing the number of living 
mollusks for most of the quantitative stations with salinity curves for 
the equivalent hydrographic stations as published by Sumner ¢# al. 
(1914) may be made. In these curves the stations are arranged along 
the horizontal axis, at distances proportionate to their relative positions 
in the bay. The average number of living mollusks from the several 
hauls made in the immediate vicinity of the hydrographic stations is 
represented along the vertical axis of the specimen curve. 
There is apparently little-correspondence between the areal density 
of the mollusks and the mean annual salinity. This is evident by 
referring to figure B. 
It appears, however, that the mean annual salinity at stations 
D 5815 to D 5820 inclusive (left end of curve) is unfavorable to an 
abundant mollusean life. The specimen curve as well as the following 
table indicates that the average number of individuals per haul is 
greatest for those stations having a mean annual salinity between 28 
and 30 per mille. 
TABLE 9 Average 
Mean number 
annual Number living 
salinity Group of hauls individuals 
17.16-19.37 il 8 3.1 
19.38—21.57 2 2 3) 
21:58-23.79 3 0 0.0 
23.80-26.07 4 6 9.0 
26.02-28.23 5 8 12.3 
28.24-30.45 6 15 82.0 
30.46—32.67 a 4 12.7 
