134 University of California Puhlications in Zoology. [Vol.8 



TABLE 45 

 Surface Distribution of S. bipunctata with Eespect to Salinity. 



These data indicate that, other things being equal, S'. hi punc- 

 tata accumulates on the surface in greater numbers when the 

 salinity of the water is between 33.605 and 33.648. It may be 

 objected that other things are not equal, that the average tem- 

 perature corresponding to each salinity group differs, and that 

 consequently the variations in abundance and frequency noted 

 in the table are due to temperature and not to salinity. How- 

 ever, it has already been shown that the species is more abund- 

 ant and frequent when the temperature is low. Therefore, if 

 salinity has no effect, M'e should expect, as shown by temperature 

 averages given in the table, the species to have been most 

 abundant and frequent when the salinity was less than 33.605 

 and least abundant and frequent when it was between 33.605 

 and 33.648. This is obviously not the case. In fact the rela- 

 tions shown between temperature averages and salinity suggest 

 that the effect of temperature is antagonistic to that of salinity. 

 If this is true, then, by including only those hauls made when 

 the temperature varied from 17?6 to 19?5 we should expect 

 greater difference in abundance and frequency with respect to 

 the three salinity groups than that found in the above data. 

 The following table demonstrates that this is true. 



Comparing this with the preceding table, we see that the 

 frequency and abundance corresponding to salinities less than 



