70 PROTOZOA chap. 



composed largely of Textularia and allied forms, mixed with the 

 skeletons of Coccolithophoridae (pp. 113-114), known as Cocco- 

 liths, etc. The Calcaire Grossier of Paris, used as a building 

 stone, is mainly composed of the shells of Miliolines of Eocene 

 age ; the Nummulites of the same age of the Mediterranean basin 

 are the chief constituent of the stone of which the Pyramids of 

 Egypt are built. Our own Oolitic limestones are composed of 

 concretions around a central nucleus, which is often found to 

 be a minute Foraminiferous shell. 



The palaeontology of the individual genera is treated of in 

 Chapman's and Lister's recent works. They range from the 

 Lower Cambrian characterised by perforated hyaline genera, 

 such as Lagena, to the present day. Gigantic arenaceous forms, 

 such as Zoftusia, are among the Tertiary representatives ; but 

 the limestones formed principally of their shells commence at 

 the Carboniferous. The so-called Greensands contain greenish 

 granules of " glauconite," containing a ferrous silicate, deposited 

 as a cast in the chambers of Foraminifera, and often left exposed 

 by the solution of the calcareous shell itself. Such granules 

 occur in deep-sea deposits of the present day. 1 



3. Heliozoa 



Sarcodina with radiate non-anastomosing pseudopodia of gran- 

 ular protoplasm, each with a stiff axicd rod passing into the body 

 plasma ; no central capsule, nor clear ectoplasm ; skeleton when 

 present siliceous ; nucleus single or multiple ; contractile vacuole 

 (or vacuoles) in fresh-water species, superficial and prominent at the 

 surface in diastole ; reproduction by fission or budding in the 

 active condition, or by brood-formation in a cyst, giving rise to 

 resting spores ; conjugation isogamous in the only two species fully 

 studied; habitat floating or among weeds, mostly fresh ivater. 



1. Naked or with an investment only when encysted. 



Aphrothoraca. Actinolophus F.E. Sch. ; Myxastrum Haeck. ; 

 Gymnosphaera Sassaki ; Dimorpha (Fig. 37, 5, p. 112) Gruber ; 

 Actinomonas Kent ; Actinophrys Ehrb. ; Actinosphaerium St. ; 

 Camptonema Schaud ; Nuclearia Cienk. 



1 The alleged Archaean genus Eozoon, founded by Carpenter and Dawson on 

 structures found in the Lower Laurentian serpentines (ophicalcites), and referred 

 to the close proximity of Nummulites, has been claimed as of purely mineral 

 structure by the petrologists ; and recent biologists have admitted this claim. 



