ORDER I 



FORAMINIFERA 



35 



primordial spiral of three to five whorls. The rings are divided by transverse 

 partitions into small rectangular chambers, and the septa and marginal cord are 

 traversed by canals. Superimposed over the median series of prinripal 

 chambers on both sides are several layers of flattened secondary chamberlets, 



FIG. 45. 



A, Orbitoides papyracea, Boubee. Eocene (Ferruginous sandstone) ; Kressenberg, Upper Bavaria. (Greatly 

 enlarged). 1 Median chambers ; a Lateral chambers ; Compact pillars of intermediate skeleton. B, Portion of 

 miMlian transverse section, highly magnified; -Lateral chambers with perforate walls; 4 Canal-system of 

 cyclical marginal cord ; 5 Tubules connecting adjacent chambers. C, Periphery and profile of same, natural 

 size. D, Orbitoides tenella, Giimbel. Eocene ; Kressenberg. (Natural size.) E, Orbitoides variecostata, Giimbel. 

 Eocene ; San Martino, near Verona. (Natural size.) F, Orbitoides ephippium, Sow. Eocene ; Kressenberg. 

 (Natural size.) 



which are likewise disposed in concentric rings. Very abundant in the Eocene, 

 associated with Nummulites ; rare in Upper Cretaceous and Miocene. 



Dawson, Carpenter, and various other authors have referred the so-called 

 Eozoon occurring in crystalline limestone of the Archaean (Laurentian) period 

 to the Foraminifera ; but the elaborate investigations of Mobius have shown 

 that neither Eozoon nor Archaeospliaerina can be regarded as organic structures, 

 but are mineral segregations. 



Range and Distribution of Fossil Poraminifera. 



Of the over 2000 species of Foraminifera that have been described, 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 silicious shell-bearing genera (Placopsilina, Saccamina), and in part to 

 vitreo-perforate genera (Nodosaria, Lagem, Globigerina, Eotalia). The Devonian 

 is also very poor in Foraminifera remains ; but, on the other hand, the Carbon- 

 iferous yields an abundant and considerably varied fauna; in fact, certain 

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



