ORDER III 



RADIOLARIA 



41 



etaceous, Textalaria, Eotalia, Cristelläria, Globigerina, Miliola and coccoliths are 

 sential constituents of the AYhite Chalk. Individual beds of the Maestricht 

 Chalk consist almost entirely of Calcarina remains ; in the Urgo-Aptian Orhi- 

 tolina is the chief rock-builder ; in the Upper Cretaceous Alveolina. 



The maximum development of the Foraminifera occurs in the Tertiary 

 period. Massive beds of the Eocene Calcaire Grossier of the Paris basin and 

 in the Pyrenees are composed of Miliolidae remains ; other Eocene limestones 

 consist of Alveolina, Operculina, Orbitolites and Orbitoides aggregations. But of 

 far greater geological importance are the Nummulites, which occur in incredible 

 abundance in the Eocene and Oligocene Nummulites-formations of the Medi- 

 terranean district, Asia Minor and Eastern Asia. 



During the late Tertiary the Nummulites almost entirely disappear ; only 

 Amphistegina continues as an occasional rock-builder, and from the middle 

 and later Tertiary on, the Foraminifera fauna remains very nearly the same 

 as now. 



[The foregoiiig chapter on Foraminifera has been revised for the preseut work by Dr. 

 Joseph A. Cushnian of the Boston Society of Natural History, Boston, Mass.— Editor.] 



Orders. RADIOLARIA Müller.^ 



{Polycystina Ehrenberg.) 



Marine FJiizopoda emitting fine, filiform, radially direded pseudopodia, with 

 central capsule and extra-capsulum, and usually with delicate siliceous skeleton. 



The sarcode body of the Radiolarians is differentiated into (1) an inner 

 central sphere or capsule of tough gelatinous-like protoplasm containing one or 



^ Literature : Ehrenberg, G., Mikrogeologie, 1854 ; also memoirs on Radiolaria from Barbados, 

 in Al)handl. Akad. Wiss. Berlin, 1872, 1875.— Haeckel, K, Die Radiolarien, lS62.—Jdem, Report 

 on the Radiolaria, in Scient. Results Cliallenger Exped., Zool., vol. xviii., 1887. — Hertwig, R., Der 



