300 University of California Puhlications in Zoology [Vol. 13 



succeeded by Lieutenant-Commander H. B. Soule, U. S. N., during 

 the years of 1912 and 1913. Much assistance has been received from 

 Dr. Sumner and from Professor Kofoid, who upon Dr. Sumner's 

 resignation has had supervision of the work. A report by Sumner, 

 Louderback, Schmitt, and Johnston (1914) has been published in 

 which the physical conditions of the waters of San Francisco Bay are 

 ably presented. The data for each dredging station in that paper 

 have served as the basis for the discussion of the Mollusca that follows. 



A portion of the general results of the studies made upon the shell- 

 bearing Mollusca dredged by the "Albatross" in San Francisco Bay 

 lends itself for a sej^arate treatment preliminary to a general dis- 

 cussion of the molluscan fauna as a whole, and is herein presented. 

 These results have to do with the so-called "quantitative" stations or 

 "orange-peel bucket dredge hauls," which comprise forty-three out 

 of a much larger total number of dredgings. 



The orange-peel bucket dredge had not been previously used for 

 biological exploration. Other devices of somewhat similar character 

 have been employed by Petersen (1913, p. 3) whereby a definite 

 amount of the bottom material could be obtained, thereby giving a 

 quantitative measure of the number of organisms living within a 

 definite area at a given locality. The orange-peel bucket dredge, de- 

 scribed and figured by Sumner et al. (1914, p. 7), has proved very 

 efficient. Regarding it, the authors state: "Its chief advantage lies 

 in the taking of comparatively large masses of mud from a single spot, 

 and particularly in the penetrating power of the apparatus which 

 renders possible the capture of deeply burrowing annelids, lamelli- 

 branches, etc." Its capacity is given as 21/2 cubic feet. Since its 

 diameter is 3.16 feet, it encloses a circular area containing 7.8 square 

 feet. 



The material collected by means of this apparatus was carefully 

 sorted and all of the macroscopic organisms preserved in formalin or 

 in alcohol. At those stations where a considerable amount of material 

 was obtained the following method of procedure was employed. All 

 of the molluscan material from such hauls was first passed over a 

 sieve of 5 millimeters mesh. The shells that remained in the sieve 

 were identified, counted, measured, and the condition of the specimens 

 was noted. The measurements consisted of the maximum, minimum, 

 and modal lengths for each species in the haul. The fine material 

 which passed through the sieve was thoroughly mixed and then quar- 

 tered after the manner of taking ore samples. A convenient sample 

 was then sorted and subjected to the same type of analysis as out- 



