i8 



DISCOVERY REPORTS 



BATHYMETRICAL DISTRIBUTION 

 Benthic species 



The following table of benthic species gives the number of hauls and the number of specimens in parallel 

 columns at three categories of depth, 0-175 "''•' i75-35° ™- ^^^ below 350 m. The depth of 350 m. is 

 chosen as being Chun's physiological line, below which assimilation by the ph^toplankton ceases. It should 

 be borne in mind, however, that the majority of hauls are coastal, and the presence of detritus, etc., in the 

 water at the coastal stations would raise the level of penetration of the sun-rays, necessary for assimilative 

 activity, to above the 350 m. line. 



The object of the table is to show, within the limits of the present material, what species are confined 

 to one of the selected categories of depth, and to what extent other species, not so confined, increase or 

 decrease in numbers per haul in passing from one depth to another. Repeated observations of this kind 

 would reveal at what depth a species or group of species was most dense, and consequently their optimum 

 depth. This would vary with the latitude and conditions of temperature. 



A number of species have depth records as, for example, 120-200 m., which do not exactly fit the arbitrary 

 categories of depth used ; and these I have placed in the categories to which their recorded depths most 

 nearly approximate. A few species are without any record of depth, and these are excluded from Table II. 



Table II 



' Shore coll. 

 '1:3. 310-402 m. 



* I : 10. 278-500 m., i.e. one haul and lo specimens. This form is used throughout. 



^ I : II. 278-500 m. ''1:1. 88-273 ti- ^ 1 : 15. 278-500 m. 



