46 



THE FOEAMINIFERA 



The plans of growth in the Foraminifera formed 

 the basis of D'Orbigny's classification, and he 

 grouped the varioiis forms in seven orders^ (fig. 26). 

 These are given below, to afford an idea of the great 

 variation in the foraminifera! shell. 



1. MoNOSTEGA. — Body consisting of a single seg- 

 ment : shell of one chamber. Flask-shaped, as in 

 Lagena; spherical, as in Orbuliiia; cylindrical and 

 coiled, as in Cornuspira. 



MONOSTEGA CYCLOSTEGA STICHOSTEGA 



LAGENA 



ORBULINA 



rvninpi voni? Nodosaria marginulina 



HELICOSTEGA ENTOMOSTEGA ENALLOSTEGA AGATHISTEGA 



CRISTELLARIA 



DISCORBINA BULIMINA TEXTULARIA SPIROLOCULINA 



Fig. 26. — D'Orbigxy's Classification of the Foraminifera, 



ILLUSTRATED BY SELECTED TyPES. 



2. Cyclostega. — Body discoidal, composed of con- 

 centric lines of segments, simple or multiple, never 

 spiral. Examples: Oj'bitolife.s, ([/jcIocI/j/)e/ts. 



3. Stichostega. — Body composed of segments 

 disposed in a single line. Shell consisting of a linear 

 series of chambers. Straight, as in Xodosm-ia ; curved, 

 as in Marginulina. 



' Conrs Elcinenfaire dePaleoutologic ct de Geologic StratigrapJiiqtie, 

 vol. ii. p. 189. Paris, 1852. 



