230 University of Califorma Publications in Zoology (Vou. 14 
About forty species were taken at depths ranging from 6 to 16 
fathoms. None of them obtained exclusively within that depth was 
dredged at more than one station. Thus there appears also in this 
ease to be no definite relationship between distribution and depth of 
water. Highty-three species and varieties were dredged at depths 
between 16 and 68 fathoms. About 50 per cent of these forms were 
taken by the Survey exclusively at these depths. Since nearly 50 
per cent of these restricted species are listed only from the outside 
fauna, it is probable that some other factor besides depth is the con- 
trolling one. 
The deep water fauna is represented by the following species: 
Columbella gausapata, Epitoniwm ef. hindsi, Leda hamata, Nassa 
perpinguis, and Pandora filosa. They were obtained by means of the 
‘* Albatross’? bottom sampling apparatus in 815 fathoms of water west 
of the Farallon Islands. As will be noted, two of these species have 
been listed from shallow water. : 
It is evident that the three bathymetric zones represented within 
the waters covered by this report can not be divided into distinct sub- 
zones upon the basis of the presence or absence of certain mollusks. 
The very few species that according to our records are restricted to 
the particular depths considered above were either rarely dredged or 
had a distribution such as to suggest that some other factor besides 
depth was more important. It is not unlikely, however, that detailed 
quantitative studies would show that the relative abundance of indi- 
viduals of a given species varies with depth, from a maximum which 
would give a clew to the optimum depth for the species under consid- 
eration. With such data available it might be possible to recognize 
several bathymetric zones. 
INFLUENCE OF TEMPERATURE 
Temperature has long been recognized as a factor in determining 
the distribution of marine organisms, but the manner in which it 
operates in restricting the range of the life of the benthos is a much 
disputed point. It appears probable that no one principle is equally 
applicable in even a majority of cases. The northward and south- 
ward ranges of mollusks are no doubt determined in some way by the 
temperatures of the waters in which they live. Unfavorable temper- 
atures may react upon the mollusk so as to interfere with its repro- 
ductive activities or to hinder the development of its larvae. 
