1918] Packard: Quantitative Analysis of Molluscan Fauna 303 



in San Pablo Bay, reaching a minimum at Golden Gate and increasing 

 but slightly toward the lower end of the bay. The minimum seasonal 

 mean salinity for the entire bay occurs in April and May and the 

 minimum in October. The bottom salinity for the entire bay is greater 

 than the mean surface salinity throughout the year, the difference 

 between the two being the greater during April and May, when the 

 surface salinity is the lowest of the year. 



A diversified bottom is encountered, the materials ranging from 

 large stones within the Golden Gate to fine muds occurring charac- 

 teristically at the extremities of the bay. 



The Molluscan Fauna of San Francisco Bay 



The molluscan fauna obtained by means of the orange-peel bucket 

 dredge comprises twenty-three pelecypods and twelve gastropods. 

 Tliis list represents about 43 per cent of the entire molluscan fauna 

 of the bay as obtained by the other types of dredges employed by 

 the Survey. The species taken by means of the orange-peel bucket 

 dredge are: 



Cardium corbis (Martyn) Solen sicarins Gould 



Gemma gemma, var. purpura Lea Spisula catilliformis Conrad 



Hinnites giganteus Gray Tellina button! Dall 



Macoma balthica (Linnaeus) Tellina salmonea (Carpenter) 



Macoma inquinata (Deshayes) Zirfaea gabbi Tryon 



Macoma nasuta (Conrad) Crepidula nivea Adams 



Modiolus, cf. rectus Conrad Columbella gausapata Gould 



Monia macroschisma (Deshayes) Epitonium hindsi (Carpenter) 



Mya arenaria (Linnaeus) Epitonium sawinae (Dall) 



Mya California (Conrad) Nassa fossata (Gould) 



Mytilus edulis Linnaeus Nassa mendiea (Gould) 



Ostrea lurida Carpenter Nassa perpinguis Gould 

 Phacoides tenuisculptus (Carpenter) Odostomia franciscana Bartscli 



Paphia staminea (Conrad) Thais lamellosa (Gemelin) 



Pholas paeificus Stearns Turbonilla franciscana Bartsch 



Psephdia ovalis Dall Turbonilla keepi Dall and Bartsch 



Saxidomus nuttalli (Conrad) Turris, cf. ineisa (Carpenter) 

 Schizothaerus nuttalli (Conrad) 



It will be noticed that nineteen genera of pelecypods and eight of 

 gastropods are represented in this list. 



Three of the genera are represented by two or more species : 

 Macoma (3), Tellina (2), Epitonium. (2), Nassa (3), and Turtonilla 

 (2). The three species of Macoma occur quite abundantly and are 

 of interest in as much as they are found together within the same 

 dredge haul. Of these species, M. haltkica was taken in 12 hauls, or 

 at about 27 per cent of the total number of hauls ; 31. inquinata in 

 13, or 28 per cent of the total ; while the third, M. nasuta, was taken 



