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. 
Tur Mouuuscan Fauna or SAN Francisco Bay 
The mollusecan fauna obtained by means of the orange-peel bucket 
dredge comprises twenty-three pelecypods and twelve gastropods. 
This 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 sicarius Gould 
Gemma gemma, var. purpura Lea Spisula catilliformis Conrad 
Hinnites giganteus Gray Tellina buttoni Dall 
Macoma balthica (Linnaeus) Tellina salmonea (Carpenter) 
Macoma inquinata (Deshayes) Zirfaea gabbi Tryon 
Macoma nasuta (Conrad) Crepidula nivea Adams 
Modiolus, ef. reetus Conrad Columbella gausapata Gould 
Monia macroschisma (Deshayes) Epitonium hindsi (Carpenter) 
Mya arenaria (Linnaeus) Epitonium sawinae (Dall) 
Mya ealifornia (Conrad) Nassa fossata (Gould) 
Mytilus edulis Linnaeus Nassa mendica (Gould) 
Ostrea lurida Carpenter Nassa perpinguis Gould 
Phacoides tenuisculptus (Carpenter) Odostomia franciscana Bartsch 
Paphia staminea (Conrad) Thais lamellosa (Gemelin) 
Pholas pacificus Stearns Turbonilla franciscana Bartsch 
Psephdia ovalis Dall Turbonilla keepi Dall and Bartsch 
Saxidomus nuttalli (Conrad) Turris, cf. incisa (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 Turbonilla 
(2). The three species of Macoma oceur quite abundantly and are 
of interest in as much as they are found together within the same 
dredge haul. Of these species, M. balthica was taken in 12 hauls, or 
at about 27 per cent of the total number of hauls; M. inquinata in 
13, or 28 per cent of the total; while the third, M. nasuta, was taken 
