150 University of Calif ODiia Publications in Zoology. [Vol.8 



Considering all the data, the following conclusions may be 

 drawn : 



1. S. serrafodentata occurs mainly in the mesoplankton. 



2. It is maximum in abundance and frequency in the region 

 of 200 fathoms. 



3. It is rarely taken above 40 fathoms during daylight, but 

 occurs above this depth at night. 



4. The species probably migrates toward the surface when 

 twilight is very subdued, but rarely ascends above 10 fathoms. 



5. Its center of migration, or the depth in which the greatest 

 number of optimum conditions are found, is probably between 

 100 and 200 fathoms. 



6. Its exceptional occurrence on the surface is probably cor- 

 related with some unusual surface conditions, of which low 

 temperature may be one. 



DISTETBUTION OF S. LYRA 

 Of the 272 specimens of this species only four were obtained 

 from the surface. Open vertical nets obtained 61 from a variety 

 of depths below 75 fathoms, horizontal closing nets obtained 112 

 from below 25 fathoms, and vertical closing nets obtained 94 

 from below 50 fathoms. All these data agree that the species 

 occurs very rarely near the surface. The exact way in which the 

 number of specimens obtained with surface and horizontal clos- 

 ing nets were distributed with respect to depth is given in the 

 following table : 



TABLE 58 



Vertical Distribution of S. lyra based on Surface and Horizontal 



Closing Net Hauls. 



The per 10 hour column is supplied in order to eliminate the fractions 

 which occur when the number of specimens is expressed according to one 

 hour hauls. 



