186 THE FOEAMINIFEEA 



Many of the genera belonging to the family 

 Lagenid.e include a large number of known specific 

 types, as Nodosaria, containing about 140, and 

 Cristellaria about 160, well-defined forms. Their dis- 

 tribution as a group is very extensive throughout the 

 fossiliferous strata of the earth's crust, and some of 

 the earliest knowm types belong to this group of 

 vitreous-shelled Foraminifera. 



The sub-family Lagenin^e includes only one genus, 

 Lagena. This is typically monothalamous and pre- 

 sents a great variety of forms, some of which are 

 flask-shaped, with an extended neck-like orifice (ecto- 

 solenian), or having an aperture at the end of an 

 inverted neck, which is turned into the chamber and 

 concealed by the shell (entosolenian). Other species, 

 again, may have the flask- shaped form, but more or 

 less compressed on two opposite faces, and with the 

 normally circular aperture modified and represented 

 by a slitlike orifice. In certain forms the orifice is 

 triradiate, or even star- shaped (multiradiate). These 

 various kinds of apertures are again met with in the 

 succeeding groups of the Nodosapjin^ and the Poly- 



MOEPHININ^. 



The genera which constitute the sub-family of the 

 NoDosARHN^ are very important, on account of their 

 occurrence in considerable numbers and variety in 

 the argillaceo-calcareous strata laid down in the seas 

 of past geological times, such as those of the Lias, the 

 Gault, the Chalk, and certain Tertiary beds. At the 

 present day these Nodosarine forms are met with in 

 a few localities in tolerable abundance ; but they seem 



