26 



SYSTEMATIC ZOOLOGY 



resembling those of DifBugia, but the pseudopodia, which are 

 fine and anastomosing, may be protruded between the foreign 

 particles of which the shell is composed. The chitinous shells 

 are well illustrated by the fresh-water Arcella (Fig. 4), 







3.!Modosaric 



\S'i6(fT'(3l]f3JS 



5. Spirolocuhna 



2.Lagena 



4.Frondicularia 6.Globigerina 



A«fr„ 



7. Discorbina 



Planorbulina 



ll.Nummulites 



Fig. 6. Shells of Foraminifera. a, aperture of shell ; 1-15, successive cham- 

 bers, 1 being in each case the initial chamber and hence the oldest. In figures 3, 

 4, and 5, a is a surface view, and b a section ; 8a, diagram of a coiled shell with- 

 out supplemental skeleton ; 8b, with supplemental skeleton, s.sk\ 10, with over- 

 lapping chambers; na, the upper half in horizontal section, the lower half in 

 surface view; nb, in vertical section. (After Carpenter, Brady, and Biitschli.) 



with its blunt pseudopodia, and by Gromia (Fig. 5), with 

 its fine anastomosing pseudopodia ; in the latter genus the 

 protoplasm extends over the outer surface of the shell in a 

 thin layer, so that the skeleton thus comes to lie internally. 

 The calcareous shells are the most numerous and the most beau- 



