22 



PROTOZOA RHIZOPODA 



CLASS I 



mollusks, corals, bryozoans, coccoliths, radiolarians, diatoms, sponges, and 

 Foraminifera. Of the latter, certain genera are remarkable for their extra- 

 ordinary abundance (Globigerina, Orbulina, Pulvinulina, Biloculina), (Fig. 10). 



In the Atlantic and Pacific Oceans Gloligerina ooze is the prevailing deep- 

 sea deposit ; in the North Sea, along the coast of Norway, Bilociilina ooze. 

 Numerous limestones and marls of older geological periods exhibit great 

 similarity in structure and chemical composition to the now forming deep-sea 

 oozes. White chalk (Fig. 11) is clearly a variety of abyssmal ooze, from which 

 silicious constituents have become segregated out, and in which Textularia 

 predominate instead of Globigerina. Certain of the Eocene limestones of the 



Specimen of prepared white chalk from Meudon, as seen in 

 transmitted light under power of 300 diameters, showing Textularia, 

 Globiyerina, and Rotalia. 



FIG. 12 



Thin slice of Pliinerkalk from Bohemia 

 viewed in transmitted light under power 

 of 50 diameters, showing sections of 

 Nodosaria, Rotalia, Frondiculcrin. and 

 numerous isolated Globigerina chambers. 



Paris basin are composed almost exclusively of the tests of Miliolidae, while 

 others are made up of Alveolinae, and Nummulites. During the Carboniferous 

 period the chief rdle as rock -building organisms was played by Fusilina. 

 Many dense, apparently homogeneous, or even semi-crystalline limestones of 

 various ages, when examined microscopically in thin sections, are seen to be 

 composed in large part of Foraminifera and other organic bodies (Fig. 12). 



Fossil Foraminifera are best preserved, being usually detachable from the 

 matrix, and at the same time occur most abundantly, in unconsolidated marls and 

 clays which are interbedded with calcareous strata, or in limestones of a chalky 

 or earthy character. 



The tests of Foraminifera were first discovered by Janus Plancus, in 1730, 

 on the beach of Rimini, and in the following year they were found by Beccari 

 in the Pliocene of Bologna. They were long considered to be shells of 

 mollusks, and were described by Breyn, Soldani, Fichtel, d'Orbigny, and 

 others as Cephalopoda foraminifera, in distinction from Cephalopoda siphonifera. 

 Dujardin, in 1835, was the first to recognise their true character as belonging 

 to the Rhizopoda, 



