21 



Table IV 



ECOLOGICAL 



Table V, with the number of specimens and the number of hauls of each species 

 arranged in parallel columns under each of the several kinds of bottom, shows within 

 the scope of the present material what species are confined to any one kind of 

 bottom, to what extent other species not so confined display an increase or decrease in 

 numbers per haul in passing from one kind of bottom to another and, consequently, 

 their relative density on the several kinds of bottom. Although the present material 

 forms a wholly insufficient basis for generalisation, repeated observations of this nature 

 should reveal the kind of bottom on which a species or group of species is most dense 

 and, therefore, their optimum bottom. If to this were added a knowledge of their 

 optimum depth, we should possess some of the factors constituting at a given latitude 

 their optimum habitat. 



The nature of the bottom is taken from the observations made by the naturalists and 

 recorded in the Station List 1925-1927 (Discovery Reports, i, pp. 1-140). For the 

 purposes of the table I have simplified their classification of the bottom deposits : grey or 

 green mud is treated as mud without qualification ; " sand, stones and rock " is treated as 

 "sand and stones"; "mud, sand and stones" is treated as "mud and sand," and so on. 

 In the table there are eight categories of bottom deposit used: mud, sand, stones, rock, 

 mud and sand, mud and stones, mud and rock, sand and stones. 



The number of species or varieties having a record of the kind of bottom on which 

 they were found is 168. 



