232 



THE PROTOZOA 



just before. Hence a distinction must be drawn between mono- 

 thalamous or single-chambered shells and polythalamous shells, 

 made up of many chambers formed successively. In the latter 

 type the new chambers may be joined in various ways to the old, 



I.Saccammina 



2.Lagena 



3-Nodosaria 



4.Frondicu!aria 6.Clobigerina 



7. Discorbina 



O.PIanorbulina 10 ll.Nummulires 



FIG. 93. Shells of various genera of Foraminifera. In 3, 4, and 5, a shows the 

 surface-view, and b a section ; 8a is a diagram of a coiled shell without supple- 

 mental skeleton ; 86, of a similar form with supplemental skeleton (s.sk.) ; 

 10, of a form with overlapping whorls ; in 11 a half the shell is shown in hori- 

 zontal section ; b is a vertical section. In all the figures a marks the aperture 

 of the shell ; 1 to 15, the successive chambers, 1 being always the oldest or 

 initial chamber. From Parker and Haswell. 



producing usually either a linear or a spiral series, and the utmost 

 variety of shape and pattern results in different species (Fig. 93). 

 Some polythalamous species exhibit a peculiar dimorphism (Fig. 94) ; 



