310 University of California Publications in Zoology [Vou.18 
On the Massachusetts coast spawning occurs from June 1 to Sep- 
tember 1. There is considerable local difference in the spawning 
season due to the fact that “‘spawning will not take place until the 
water has attained a warmth suitable for the development of young 
larvae’’ (Mass. Com’rs of Fisheries and Game, 1916, p. 105). It does 
not necessarily follow that the spawning season of San Francisco Bay 
would be the same time, for the water temperature may be suitable 
for reproduction during other months of the year. This problem 
should be investigated, since it has an economic as well as a scientific 
significance. 
It is evident that the larval stage of the clam is the most critical’ 
period of its life. Durimg this stage it is defenseless, subject to the 
varying conditions of surface temperature and salinity and to the 
tidal currents. If the young clams drift away from a suitable bottom 
they are destroyed in countless numbers, or the currents may sweep 
many together so that many more become attached within a small 
area than can possibly develop. 
It is highly desirable to determine the localities within San Fran- 
cisco Bay where the set is heavy from year to year, for such places 
would supply young clams for transplanting to localities less favorably 
situated as regards tidal currents. 
Paphia staminea occurs commonly on sandy bottom. It, too, is a 
hardy form, occurring within estuaries as well as along the sandy 
beaches of the open ocean. Apparently San Francisco Bay does not 
afford as suitable conditions for the development of this clam as 
for the preceding species, since it was more rarely taken by the 
“* Albatross’’. 
Saxidomus nuttalld is not abundant within San Francisco Bay, 
occurring, according to the Survey records, only within the Golden 
Gate. This species is elsewhere more frequently taken from a sandy 
and gravelly bottom, into which it burrows deeply. It is found along 
the open ocean and within inlets within which the range of salinity 
is not great. This large clam is quite abundant along Oregon and 
Washington shores, where it is taken in considerable numbers. This 
species, together with the following, possesses a dark epidermis around 
the large muscular siphon, which detracts from the appearance of the 
clam and which must be removed before it is canned. 
Schizothaerus nuttalli burrows very deeply in the muddy sand of 
the open ocean or bays. It was taken alive but once within San 
Francisco Bay, probably because the dredge failed to sink deep enough 
