24 PROTOZOA— EHIZOPODA phylüm 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 Textularia 

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

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

 others are made up of Älveolinae and Nummulites. During the Carboniferous 

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

 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 sipfionifera. 

 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 pseudopodia. 



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 tubulär 

 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. 



Becent and very abiindant at depth. Fossil in Paleozoic and later 

 formations. 



Subfamily A. Astrorhizinae Brady. 



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

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



The genera Astrorhiza, Bhabdammina, Marsipella, Bathysiphon and 

 Rhizammina 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 agglutinated material ; apertures sometirnes 

 numerous but usually single ; tests free or attached. 



