FORAMINIFERA. 



99 



The pseudopodia reach the exterior either ly perforations in 

 the walls of the shell, or simply ~by the mouth of the latter 

 (fig. 13, c I). 



Fig. 13. Morphology of Foraminifera. o, iTtfj/oia vulgaris, a monothalamous Foraminifer ; 

 7>, Miliola (after Schultze), showing the pseudopodia protruded from the oral aperture of the 

 shell ; c, Discorbina (after Schultze), showing the nautiloid shell with the foramina in the 

 shell-wall giving exit to pseudopodia ; d, Section of Nodosaria (after Carpenter) ; e, Nodosaria 

 hispida; f, Globigerina bullaides. 



From a palseontological point of view the only part of a 

 Foraminifer with which we have to deal is the shell or 

 " test/' and there are several points to notice in this connec- 

 tion. Firstly, as regards the actual composition of the shell, 

 it is in the majority of cases calcareous, or composed of 

 carbonate of lime, but it is rarely chitinous, and it is not 

 uncommonly " arenaceous " that is, composed of particles 

 of sand cemented together by some animal substance or 

 by carbonate of lime. With the horny or chitinous Fora- 

 minifera (Gromidce) we have nothing to do here, as they have 

 never been, and are never likely to be, detected in a fossil 

 condition. 



In the second place, the Foraminifera may be divided into 

 two primary groups the Perforata and Imperforata accord- 

 ing as the walls of the test are or are not perforated by pores 

 or foramina, through which the pseudopodia reach the surface. 

 In the imperforate calcareous Foraminifera the substance of 



