24 PROTOZOA— RH I ZOPODA phylum i 



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

 oozes. White Chalk (Fig. 6) is clearly a variety of abyssal ooze, from which 

 siliceous constituents have become segregated out, and in which Textnlaria 

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

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

 others are made up of Alveolinae and Nimimulifes. During the Carboniferous 

 period the chief role as rock-building organisms was played by Fusnlina. 

 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. 7). 



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. 



Family 1. Gromidae. 



Test chitinous with an aperture at one or both ends for the pseicdopodia. 



The animals belonging to this family are mostly fresh-water species and 

 their occurrence as fossils is unknown. 



Family 2. Astrorhizidae Brady. 



Test composed of agglutinated material for the most part, occasionally with a 

 chitinous inner layer, consisting of a chamber with several openings or a tubular 

 test open at both ends ; or in certain forms of a closed chamber with a single 

 aperture. Throughout the family the test is not divided into a series of chambers. 



Recent and veiy abundant at depth. Fossil in Paleozoic and later 

 formations. 



Subfamily A. Astrorhizinae Brady. 



Test consisting usually of a tube open at both ends or ivith several tubes entering 

 a central chamber ; in some species with the tube branching. 



The genera Astrorhiza, lihabdatamina, Marsipella, Jiathysiphon and 

 Bhizammina make up this subfamily. Apparently fossil since the Upper 

 Jurassic and common in Recent. 



Subfamily B. Saccammininae Brady. 



Test consisting of a single chamber, or group of superficially attached chambers. 

 The walls made up for the most part of ((gglufinatrd material ; apertures sometimes 

 numerous but usually single ; tests free or attached. 



