THE 



VOYAGE OF H.M.S. CHALLENGEE. 



ZOOLOGY. 



KEPORT on the Ostracoda dredged by H.M.S. Challenger during the years 

 1873-1876. By G. Stewardson Brady, M.D., F.L.S. 



INTRODUCTOEY. 



The extreme depths of the sea, though supporting au abundance of animal life of 

 many kinds, nevertheless present conditions very unfavourable, it would seem, to the 

 existence of the particular group which forms the subject of this report. So that in 

 those large abyssal areas where, as commonly happens, the ocean-bed consists of pure 

 globigerina ooze or of " red clay," one searches usually in vain for traces of Ostracoda ; 

 and when these do occur their numbers are extremely small, the specimens usually con- 

 sisting of detached valves, frequently much worn or broken. It would not, however, be 

 fixir to assume from these appearances that the specimens had been transported, by currents 

 or otherwise, from shallower waters, — still less that they had subsided, as is probabledn 

 the case of many Foraminifera, from the water above ; seeing that the species found in these 

 abysses are usually quite incapable of swimming. We must, therefore, conclude that 

 Ostracoda do live, though in very limited numbers, in the most profound depths of tlie sea. 

 Tlie list given below includes the names of all species found in dredgings beyond a 

 depth of 500 fathoms, the total number being fifty-two species from twenty-nine 

 dredgings, the number of individuals being likewise very small. And if we exclude from 

 consideration all but the very greatest depths, from 1500 fathoms downwards, the paucity 

 of species becomes still more apparent. To exhibit this clearly, I print a list of the 

 species found in thirteen dredgings, from depths of more than 1500 fathoms; the 

 number of species here is nineteen,^ a result sufficiently striking when compared with 

 such single shallow- water dredgings as that from near Booby Island (see list, p. 21), 

 which shows twenty-eight species ; from Torres' Straits (p.^21), nineteen ; Balfour Bay, 

 Kerguelen Island (p. 16), nineteen; or Port Jackson (p. 19), twenty-three species. 



1 Two out of the nineteen are species of Halocypris, which in all probabilitj' got into the di-eilge during the 

 process of hauling in, so that the number might not unfairly be put down'as seventeen. 



(ZOOL. CHALL. EXP. — PART III. — 1880.) C 1 



