FORAMINIFERA. 1 37 



with the Nummulitic Limestone of the Eocene. Thus they form 

 whole beds of the Carboniferous Limestone in Russia, Central 

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

 Though pre-eminently Carboniferous, they occur also in the 

 Permian. 



The remaining types of the Nummulinida can be merely al- 

 luded to here. The genus Orbitoides is extremely like Nu??wiu- 

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

 taken for it, but it differs considerably in its internal structure, 

 and especially in the fact that its mode of growth is cyclical in- 

 stead of spiral, and the place of the " alar prolongations " 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 Nummulina, an extraordinary devel- 

 opment 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 

 Cyclodypeus, 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 

 Rotaline type. The genus commences in the Upper Cretaceous, 

 but is particularly developed in the Eocene of the South of Europe 

 and Africa. Lastly, Heterostegi?ia (Tertiary and Recent) differs from 

 Operculi?ia chiefly in having the principal chambers broken up into 

 chamberlets by secondary septa. 



APPENDIX TO FORAMINIFERA. 



Eozoon Canadense. 



In connection with the subject of the Forami?iifera, it is necessary to 

 consider the structure and probable nature of the singular body to which 

 the name of Eozoon has been given, since this body, if organic at all, 

 must be regarded as referable to the foregoing group of organisms. 

 There is, in fact, a special, twofold interest attaching to Eozoon, if it 

 should be proved that the body so named is truly organic. In that case, 

 Eozoon would, on the one hand, be the most ancient type of life which 

 has yet been detected by the researches of palaeontologists, while, in the 

 second place, it would present us with a type of Foraminifera of colossal 

 size, and in other respects of quite peculiar zoological interest. Since the 

 whole subject of the structure and relations of Eozoon is one of great 

 complexity, it would not be advisable to deal with it here in any detailed 

 manner, or to enter into the long and still unfinished controversy which 

 has been carried on as to the organic or inorganic nature of this remark- 

 able body. It will be sufficient to briefly describe the general form and 



