REPORT ON THE ISOPOD A. 159 



Table IV. — 2000 fathoms and upwards. 



Eurycope abyssicola, F. E. B. 



„ intermedia, F. E. B. 

 Arcturus abyssicola, F. E. B.; III. 

 Baihytanais bailiybvotes, F. E. B., shallow 



water. 



Typhlotanais sp., F. E. B. 



„ brachyurus, F. E. B. 



Serolis nesera, F. E. B.; II. 



It is clear from the above tables, that as the depth increases there is less similarity 

 between the Isopodan fauna, and that of shallow water. 



In Table I., from 300 to 500 fathoms, there are twenty-three species recorded; of these 

 no less than eleven or nearly one-half also range into shallow water, in many instances 

 into such insignificant depths as 50 fathoms ; six of these species on the other hand are 

 also found in greater depths, but of these six, only three extend into the shallower regions 

 of the ocean ; nine are peculiar. 



In Table II., from 500 to 1000 fathoms, there are seventeen species; three of these 

 are found both in Table I. and in shallow water, and another is found in Table I. but 

 not in shallow water, three other species range into greater depths ; ten are peculiar to 

 depths of from 500 to 1000 fathoms. 



In Table III., from 1000 to 2000 fathoms, there are twenty-nine species, of which, how- 

 ever, five were dredged in water of from 1000 to 1070 fathoms, and therefore only just 

 fall within the limits assigned. Only a single species is also an inhabitant of shallow 

 water ; three range into less depths, and one into greater depths. 



In Table IV., there are seven species, of which four only exceed by a few fathoms the 

 limits assigned to this table, two range into less depths, another (perhaps two) into 

 shallow water, while three are only to be found in this table. 



In passing from the lesser to the greater depths, there is evidently, as has been stated 

 above, a decreasing number of species that are common to these depths and to shallow 

 water ; but it is impossible to draw an absolute line of division which would separate an 

 abyssal from a shallow- water fauna; the two overlap each other throughout; it may be 

 safely stated, however, that the greater the depth at which a given Isopod occurs, the 

 less chance there is of its being also an inhabitant of shallow water and vice versd. It 

 will also be seen from the above tables that the largest number of deep-sea species occur 

 in Table III., that is, in depths of from 1000 to 2000 fathoms, and of these species twenty- 

 four are peculiar to that zone, including six distinctive genera. In the very great depths 

 there is a great falling off in the number of species. 



There is no trace of any zone that is without its Isopod fauna ; from 345 fathoms up 

 to 2740 fathoms species were dredged continuously ; there is nowhere a break of more 

 than 100 fathoms. 



