FORAMINIFERA 



6l 



marks, or on the so-called littoral shelf extending to deep water ; 

 they are for the most part adherent to seaweeds, or lie among 

 sand or on the mud. Other forms, again, are pelagic, such as 

 Globigerina (Figs. 13, 6, 16, 17) and its allies, and float as part 

 of the plankton, having the surface of their shells extended by 

 delicate spines, their pseudopodia long and radiating, and the outer 



Fig. 12. Lieberkiihnia, a fresli-water Rliizopod, from the egg-shaped shell of which 

 branched pseudopodial filaments protrude. (From Verworn.) 



part of their cytoplasm richly vacuolated (" alveolate "), and pro- 

 bably containing a liquid lighter than sea water, as in the Kadiolaria. 

 Even these, after their death and the decay of the protoplasm, 

 must sink to the bottom (losing the fine spines by solution as they 

 fall) ; and they accumulate there, to form a light oozy mud, the 

 " Globerina-ooze " of geographers, at depths where the carbonic 

 acid under pressure is not adequate to dissolve the more solid 

 calcareous matter. Grey Chalk is such an ooze, consolidated by 



