208 University of California Publications in Zoology |Vou.14 
was divided into two classes, herein designated the ‘‘qualitative’’ or 
the ‘‘quantitative,’’ depending upon whether the collection was made 
by one of several common types of dredges or by the orange-peel bucket 
dredge, which was employed here for the first time for biological 
purposes. The records of these quantitative hauls are meluded in 
this paper, but these data are incorporated only in part in the dis- 
cussions. 
The qualitative material has been made the basis for this paper. 
The mollusks from each station were identified, measured, counted, 
and their condition noted. The identifications have been facilitated 
by comparison with a typical set from the collection that had been 
determined by Dr. W. H. Dall and Dr. Paul Bartsch, of the United 
States National Museum. The maximum, minimum, and modal lengths 
for each species were recorded for each station. A record of the 
number of specimens (of the number of valves in the case of dead 
pelecypods) was likewise made for each species. The condition of 
each specimen, i.e., whether it was living at the time of dredging, or 
was represented by a worn shell, was also noted. 
In the systematic portion of this paper no attempt has been made 
to give a complete synonymy for each species, but at least one refer- 
ence includes such a synonymy. The synonyms listed include the 
names under which the species was originally described and the more 
common ones found in the literature dealing with the region of San 
Francisco. Complete titles of works cited may be found in the 
bibliography at the end of this paper. 
The original descriptions of the species are quoted whenever it 
seemed practicable. For those that were origimally described in a 
foreign language, a subsequent description by an author who has 
given a concise diagnosis of the form in English is used. The dimen- 
sions given are the minimum and maximum length of all the specimens 
of the species which were obtained by the Survey. 
The italicized type in the parentheses following the number of the 
dredging station indicates the number of living specimens of the 
species obtained at that station, while the arabic number indicates 
the number of valves, in the case of pelecypods, or the number of 
specimens of other mollusks that were dead at the time of dredging. 
This catalogue of species includes the forms taken by the Survey 
and those that have been reported from San Francisco and vicinity 
by other workers. Zittel’s Textbook of Palaeontology, 1912, Kastman 
translation, has been used primarily for the classification employed. 
