of Edinburgh, Session 1879 - 80 . 
509 
Bathymetrical Distribution of the Calcareous Shells and Skeletons 
of Surface Organisms. — Although these lime -secreting organisms 
are so abundant in tropical surface waters, their cast-off shells and 
skeletons are either wholly or partially absent from by far the 
greater part of the floor of the ocean. In depths greater than 3000 
fathoms we usually met with only a few shells of Pelagic Fora- 
minifera of the larger and heavier kinds ; a few hundred fathoms 
nearer the surface they became more numerous, and we get a few of 
the smaller kinds and some Coccoliths and Rhabdoliths. At about 
1900 or 1800 fathoms a few shells of Pteropods and Heteropods 
are met with ; and in all depths less than a mile we have a deposit 
in which the shell and skeletons of almost every surface organism 
is to be found. In the equatorial streams and calms the calcareous 
Algae, Pelagic Foraminifera, Pteropods, and Heteropods are more 
abundant on the surface than elsewhere; and it is in these same 
regions that we found their dead shells at greater depths than in 
Orbulina universa. 
Globigerina bulloides. 
,, cequilateralis. 
,, sacculifera (hirsuta). 
Globigerina dubia. 
,, rubra. 
,, conglobata 
, , inflata. 
It is the dead shells of these Pelagic Foraminifera which chiefly make up the 
calcareous oozes of the deep sea. The living shells of all the above varieties 
swarm in the tropical and sub-tropical waters near the surface. It is especially 
in the region of the equatorial calms that the largest and thickest shelled speci- 
mens are found. As we go north or south into colder water they become smaller, 
and many varieties die out. In the surface waters of the Arctic and Antarctic 
regions, only some dwarfed specimens of Globigerina bulloides are met with. The 
author is unable to agree with Dr Carpenter and Mr Brady in thinking that 
these Pelagic Foraminifera also live on the bottom. This question was made 
the subject of careful investigation during the cruise. The shells from the sur- 
face and from the bottom were compared at each locality, and it was found, 
by micrometric measurement, that surface specimens were as large and as thick 
shelled as any average specimens from the soundings. It is quite unlikely 
that the same individuals should pass a part of their lives in the warm sunny 
surface waters, at a temperature of from 70° to 80° Fahr., and another part in the 
cold dark waters two or three miles beneath, at a temperature of 30° or 40° 
Fahr. The geographical distribution of these Pelagic forms over the bottom 
coincides, exactly with the distribution of the same forms on the surface ; that 
is to say, both on the surface and on the bottom, the distribution is ruled by 
surface temperature. No specimens of these Pelagic varieties were ever ob- 
tained from the bottom with the shells filled and surrounded with sarcode. 
Whereas creeping and attached forms (like Truncatulina, Discorbina, Anoma- 
lina, and some Textularise) were taken in this condition in almost every dredge. 
These last-mentioned forms which we know live on the bottom have a distri- 
bution quite independent of surface temperature. 
