40 THE FOEAMINIFERA 



that of the recent porcellanoas forms of the genus. 

 The group of the iniperforata is chiefly comprised 

 within H. B. Brady's family of the Miliolid.e. 



'2. Pe if Grata or Hijaliiia. — These forms have a 

 shell-wall which is perforated by minute tubes 

 that pass to the external surface of the shell. 

 The sarcode is extruded through these tubulin 

 and more or less covers the outer surface of the 

 shell in the living animal, breaking up into reticu- 

 lating and anastomosing pseudopodia ; or in other 

 cases is extruded directly from the tubuli as line 

 threadlike pseudopodia. The sarcode is also, as 

 in the previous group, extruded through the aper- 

 ture on the last septal face, and by other apertures 

 which may exist on the external surface, such as 

 the lateral series of perforations in Polystomella. 

 The shell texture of this group is usually trans- 

 parent and glassy, hence the term liyaUna. The 

 shell itself is composed of carbonate of lime in the 

 form of calcite. 



This group comprises the remainder of the 

 Foraminifera, with the exception of the families of 

 the Geomiid.e, the AsTROEmziu.E, the Lituolid^e, and 

 a part of the family of the Textulaeiice. 



3. Arenacea. — This group is distinguished from 

 the two previous in having a test not secreted by the 

 organism, but constructed by it from adventitious 

 particles picked up from its surroundings, and ce- 

 mented together by a modification of the sarcode 

 itself. In this respect it often resembles the curious 

 little cases formed by the caddis worm, as, for 



