REPORT ON THE DEEP-SEA DEPOSITS. 
263 
There are not more than twenty or twenty-two species of pelagic Foraminifera, yet 
so numerous are the individuals of the species that they usually make up over 90 per 
cent, of the carbonate of lime present in the calcareous oozes of the abysmal regions of 
the ocean. The individuals belonging to even a dozen of these species far outnumber 
the individuals belonging to all the other known genera and species of Foraminifera. 
This is true not only with regard to their abundance and great importance in the now- 
forming deep-sea deposits, hut also to their great development in Tertiary and other 
geological formations.^ 
The bottom-living Foraminifera — those belongiug to the Benthos — are more abundant 
in the shallow- water, than in the deep-sea, deposits, and occasionally a single species may 
occur in such abundance in shallow depths in some regions as to make up the greater 
part of a deposit, as, for instance, Amphistegina at the Cape Verdes, Orhitolites at the 
Fiji Islands, and Heterostegina at Amboina,^ but the extent of such deposits is very 
limited when compared with a Globigerina Ooze, or any other deep-sea deposit. When- 
ever bottom-living species of Foraminifera are, compared with pelagic species, abundant 
in a deposit, they indicate comparatively shallow water and proximity to land. The 
species of Foraminifera that live on the bottom in deep water are habitually under 
very uniform conditions,® and consequently their shells do not vary in size and thickness 
with change of latitude like those of the pelagic species, the animals of which are subject 
to great changes of temperature and salinity in the surface waters. 
Many of the arenaceous Foraminifera form their tests of minute calcareous shells of 
Globigerinidse or their fragments, together with other calcareous fragments in the sands, 
muds, clays, or oozes at the bottom, and many instances are given of the wonderful power 
of selection possessed by certain species. The tests of Pilulina and Technitella are con- 
structed of masses of Sponge spicules felted together, and the same is the case with 
Marsipella, in which the spicules are laid together side by side and strongly cemented. 
Psammosphsera, Storthosphmi'a, Pelosina, Pilulina, and Technitella are distinguished 
from each other primarily by the kind of material they individually select for the con- 
struction of the test. In the Lituolidae there is a certain amount of selective power, the 
nature of the foreign material depending more or less on the character of the sea-bottom ; 
for instance, in pure Globigerina Ooze the dead shells of the smaller Foraminifera are 
used, and in the tropics the calcareous debris of coral reefs, while the tests of Badiolaria 
and the frustules of Diatoms are sometimes employed in considerable numbers. The pre- 
ference for Sponge spicules, broken or entire, also exists among the Lituolidse. 
1 See Murray, “The Maltese Islands, with Special Reference to their Geological Structure,” Scot. Geogr. Mag., vol. 
vi. pp. 449-488, 1890. 
* See pp. 63, 89, and 97, Chapter II. 
3 The following are a few of the cosmopolitan species which extend into deep water : — Biloculiim ringem, Miliolina 
seminulum, Rotalia soldanii, Truncatulma lohatula, Nonionina umbilicatula, Nodosaria farcimen, Cassidulina crassa, 
Gristellaria rotulata, Lagena globosa, Lagena Ixvis, Lagena sulcata, &c. 
