40 PROTOZOA— RHIZOPODA phylüm i 



spirally wound segments which completely envelop one another. Eacti Seg- 

 ment is partitioned off into long, narrow Chambers by septa arranged at right 

 angles to the axis, and these are subdivided into chamberlets by a second 

 set of septa running transversely to the first set. Each of the secondary 

 chamberlets communicates with the adjacent primary Chamber by means of a 



Single round aperture. In 

 certain Eecent species the 

 secondary chamberlets are 

 also subdivided. The 



genus begins in the Ceno- 

 manian, continues in ex- 

 ^^*'- ^^- traordinary profusion, and 



Älveolinahosci d'Orh. Eocene (Calcaire Grossier) ; Paris. ^.Frontal hppnmpc: n mnQf imnnrfnnf 

 aspect. B, Test laid open so as to show conformation of iuterior ; ^^^COmes a mOSt importaut 



considerabiy eniarged. rock-builder in the Eoccne. 



It is especially abundant 

 in the Calcaire Grossier of the Paris basin, the Alveolina limestone of Istria, 

 Dalmatia, Greece and the Libyan Desert. 



Siibfamily G. Keramosphaerinae Brady, 



Test spherical, Chambers arranged in concentric layers. 



Keramosphaera Brady. Test spherical, Chambers more or less irregulär, 

 in concentric layers. Recent. 



Range and Distribution of Fossil Foraminifera. 



More than 2000 species of Foraminifera have been described, of which 

 number about two-thirds are known in a fossil State. The longevity of 

 certain genera and species is remarkable, many of them persisting, according 

 to Parker, Jones, Brady and others, throughout a number of formations of 

 various ages. 



The earliest forms occur very sparingly in the Silurian of St. Petersburg, 

 Siberia and Scotland. They are for the most part poorly preserved, those 

 from Petersburg being recognisable only as glauconitic casts, belonging in 

 part to siliceous shell-bearing genera {Placopsilina, Saccamina), and in part to 

 vitreo-perforate genera (Nodosaria, Lagena, Glohigerina, Rotalia). The Devonian 

 is also very poor in Foraminifera remains ; but, on the other band, the Carboni- 

 ferous yields an abundant and considerabiy varied fauna ; in fact, certain 

 genera (FusuUna, Schwagerina, Saccamina, Endothyra) build up limestone de- 

 posits occasionally of great thickness. Numerous representatives of the 

 Lagenidae {Nodosaria, Dentalina, etc.), Textulariidae, Rotalidae, and even the 

 Nummulitidae accompany the rock-building forms, and continue for the most 

 part throughout the Permian. Except in the Alps, the Triassic is almost 

 destitute of Foraminifera, and even the pure limestones and dolomites of the 

 Alpine Trias have usually become so altered by metamorphism as to render 

 the recognition of tests wellnigh impossible. Notwithstanding, Globigerina 

 limestone lias been discovered in the Upper Triassic of the Northern Alps, 

 and tests of Cristellaria, Marginulina, Glohigerina, Textularia, Bilocidina, etc., are 

 found in the St. Cassian beds. 



Certain argillaceous and calcareous strata of the Lias and Jura contain 

 vast quantities of minute, vitreo-perforate or siliceous Foraminifera. In the 



