No. 553] DISTRIBUTION OF THE CHJETOGNATHA 35 



The table indicates that K. subtilis maintains its maxi- 

 mum abundance between 200 and 250 fathoms, and all 

 the data agree that it does not occur above 50 fathoms. 



ElTKROHNIA HAMATA 



Two specimens of this species were taken with hori- 

 zontal closing nets from 110 fathoms, two from 300 

 fathoms, and two from 350 fathoms. The vertical closing 

 net obtained nine from between 25 and 50 fathoms, one 

 from between 150 and 200 fathoms, six from between 200 

 and 250 fathoms, and one from between 250 and 300 

 fathoms. None were obtained in open vertical hauls 

 made from above 250 fathoms. These data show that E. 

 hamata is typical of the mesoplankton, and suggest that 

 the region of maximum abundance is in the neighborhood 

 of 250 fathoms. 



The essential facts presented in this brief discussion of 

 vertical distribution may best be summed up by classi- 

 fying so far as possible the various species within the San 

 Diego region on the basis of similarities and differences 

 in their manner of distribution. When this attempt is 

 made we find that a key somewhat as follows may be 

 built up : 



Key to the Species op Ch.etognatha op the San Diego Region based 



A. Species conspicuously epiplanktonic, -\ 

 a depth of 150 fathoms 



above 100 fathoms 



BB. Species whose depth of ? maximum 



