No. 553] DISTBIBUTION OF THE CHJZTO GNA THA 33 



specific morphological characteristics, and it would be 

 quite as easy to identify the species from an analysis of 

 data regarding its vertical distribution within an area 

 analogous to the San Diego region as it would from the 

 usual taxonomic descriptions. 



Detection of specific differences in the vertical distribu- 

 tion of the remaining species is rendered more uncertain 

 because so few specimens have been obtained. However, 

 by taking the species one at a time, it will be seen that 

 tendencies, at least, toward specification are revealed. 



Sagitta planktonis 

 Eliminating those catches made with open vertical nets 

 as of little or no value in determining the depths from 

 which specimens were obtained, we find that seven S. 

 planhtonis were taken between the surface and 150 

 fathoms, two between 150 and 200 fathoms, six between 

 200 and 250 fathoms, and eleven between 250 and 300 

 fathoms. If we separate those obtained with horizontal 

 from those obtained with vertical closing nets the relative 

 abundance of the species in these various depths may be 

 expressed as in the following table : 



TABLE V 

 Relative Abundance of Sagitta planJctonis 



250-350 19 18 



This table shows that this species increases in abun- 

 dance as the depth increases and reaches its maximum in 

 the neighborhood of 300 fathoms. When we realize that 

 approximately the same relative abundance is obtained 

 from independent considerations of data supplied by 

 horizontal and vertical closing nets, this conclusion is 

 placed upon solid ground, in spite of the few specimens 



