36 



THE FOEAMINIFERA 



Feueroplis and Orhifolites ; but are represented in 

 the perforate group usually by a single opening or 

 slit placed either on the inner or outer border of 

 the shell in curved and coiled forms (fig. 21). 



The group of the Perforata, as the name sug- 

 gests, is distinguished by having a tubulated shell- 

 wall. The tubules vary greatl}^ both in number and 

 also in diameter in the various genera. Usually 

 the number of tubules varies, according to their 



Fig. 22. x 332. 



A = Coarse tubuli in the sliell-wall of Carpentei-ia ; B = fine tubuli in Amphistegiiia. 



O'l'iijiniil. 



size, in a proportionate manner ; that is to say^ 

 the coarsely tubulated shell-wall has tubules placed 

 at considerable intervals, whilst the finely perforate 

 types have the shell-wall crowded with them. Those 

 shells which have coarse tubules appear punctate 

 when the surface is examined with a lens ; but 

 surface punctations are not always indicative of 

 tubulation. An example with coarse tubuli is Cai-- 

 'penteriit, in which the perforations have a diameter 

 of •! mm, (fig. 2-2, a). The tubuli in Amjjhistegma 



