310 University of California Publications in Zoology [Vol. 13 



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. During 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 nuttalli 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, Avhere 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. 



Sdiizothaerus 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 



