‘200 
THE VOYAGE OF H.M.S. CHALLENGER. 
the genera (rlobitjerina, PulvinuUna, Sphseroidina, and Pullenia, have a pelagic mode of 
life, wliich were aforetime believed under all circumstances to inhabit the oozes at the 
bottom of the sea. All the pelagic or oceanic species, a list of which is given on page 
214, have calcareous shells; they especially flourish in the pure currents of the open 
Fi<!. 23. — Olobif/eriiia bidUjuUji, d'Orbigiiy. From tlie .surface. 
off-aii, and they arc but rarely taken in the tow-ncts in bays or estuaries or along coasts 
that arf niufh affected by river water. The annexed woodcuts show four characteristic 
njrfaeo specimens of Orbu/inn, (llohifjerina, and llaslujeHna. Nearly all the species 
are oonfined to trojdcal and subtropical waters; they gradually disappear from the surface- 
nets a.s the polar regions arc approached, the dwarfed forms Globir/erina pachyderma 
