No. 553] DISTRIBUTION OF THE CH2ET0GX A Til A 31 



still unaccounted for, were all obtained in open vertical 

 hauls from 45, 75, 110 and 290 fathoms. 



These data indicate that these three species can not be 

 regarded as typical of the San Diego region, and since 

 they occur abundantly in the surface waters of more 

 tropical seas where the temperature reaches 34° C, it 

 seems likely that they have been carried here by currents 

 from the warmer regions, although no such currents are 

 known with certainty. The probability of this supposi- 

 tion is somewhat increased because of their reoccurrence 

 here during the past winter after an absence of over two 

 years. 



Of the remaining species, S. bipunctata, 8. serrato- 

 dentata, and 8. lyra are the most typical of the San Diego 

 region. The number of each species obtained from the 

 various depths with horizontal nets is shown in the fol- 

 lowing table : 



This table reveals the fact that S. bipunctata was ob- 

 tained in by far the greatest numbers between the surface 

 and 25 fathoms, and that it was not taken at all below 150 

 fathoms. 8. serratodentata, on the other hand, appeared 

 in greatest abundance between 150 and 250 fathoms, and 

 8. lyra between 250 and 350 fathoms. However, the mere 

 tabulation of the number of specimens taken from the 

 various depths does not reveal the true significance of the 

 data, for it is obvious, from the last column, that the 

 amount of hauling, and consequently the amount of water 

 filtered, has varied with the depth so that the relative 

 density or abundance in the various depths is not repre- 



