FORAMINIFERA. 121 



which have been justly paralleled with the Nummulitic 

 Limestone of the Eocene. Thus they form whole beds of 

 the Carboniferous Limestone in .Eussia, Central Europe, 

 Armenia, India, China, Japan, and the United States. 

 Though pre-eminently Carboniferous, they ocour also in the 

 Permian. 



The remaining types of the Nummulinida, with the excep- 

 tion of the much-disputed Eozoon, can be merely alluded to 

 here. The genus Orbitoides is extremely like Nummulina 

 in external appearance and form, and has been often mis- 

 taken for it, but it differs considerably in its internal struc- 

 ture, and especially in the fact that its mode qf growth is 

 cyclical instead of spiral, and the place of the " alar prolon- 

 gations" of the chambers of the latter is taken by a multitude 

 of chamberlets. The genus appears first at the summit of 

 the Cretaceous, but it undergoes, along with its ally Num- 

 mulina, an extraordinary development in the early Tertiary 

 period, and it forms immense masses of Eocene limestone in 

 the Southern United States, the West Indies, and in various 

 parts of the Old World. A nearly allied genus is Cyclody- 

 peus, which is also coin-shaped, and is strictly cyclical in its 

 mode of growth. It occurs in the Miocene Tertiary, and 

 the only known recent types attain an extraordinary size 

 (over two inches in diameter). Operculina, again, is much 

 more closely related to Nummulina proper in its internal 

 structure, though it differs in form, owing to the fact that 

 the chambers of the spirally -inrolled shell have no "alar 

 prolongations," and thus approximate to the Eotaline type. 

 The genus commences in the Upper Cretaceous, but is par- 

 ticularly developed in the Eocene of the South of Europe 

 and Africa. Lastly, Heterostegina (Tertiary and Eecent) 

 differs from Operculina chiefly in having the principal cham- 

 bers broken up into chamberlets by secondary septa. 



Finally, if we admit that it is truly a fossil, we must 

 include here the singular body which is known as Eozoon 

 Canadense. Upon the true nature of this body a long con- 

 troversy has been carried on, into which it would be impos- 

 sible and out of place to enter here. It is sufficient to say 

 that while the highest living authorities upon this special 



