REPOKT ON THE BEEP-SEA DEPOSITS. 
259 
frequent are the shells of Foraminifera ; it maybe safely said that these organisms or 
their fragments are present in every average sample of marine mud, clay, ooze, or sand. 
For our immediate purpose the Foraminifera of marine deposits may be divided into 
two great groups according to their mode of life, one comprising all those bottom- 
living species which habitually live on or move about on the floor of the ocean, belonging 
to the Benthos, and the other comprising all those pelagic species which habitually live 
in the surface and subsurface waters of the open ocean, therefore belonging to the pelagic 
Plankton.^ 
The Challenger observations have clearly established that many species belonging to 
> These two groups of pelagic and bottom-living Foraminifera are distinguished in the Tables of Chapter II. under 
the heading “ Foraminifera ” by different estimated percentages for each group (see p. 26). 
