PROTOZOA. 163 



find many genera and species which secrete a shell or 

 external envelope of Carbonate of Lime, or Chalk. 

 These shells are often of singular beauty. They are 

 generally perforated by a large number of minute open- 

 ings for the passage of the pseudopodia, and hence are 

 termed Foraminifera, {foramen, an aperture ; fero, I 

 carry.) (Fig. 67.) Some of these foraminifera are sin- 

 gle chambers, often like striated flasks, (La gen a >) but 



FlG. 67. Rosalina ornata, with its pseudopodia extended. 



others are compound, either straight, (Nodosaria,) spiral, 

 (Rotalia,) or irregular, (Globigerina.) These shells are 

 generally microscopic, although some, as the Nummu- 

 lites, may be an inch in diameter, and the fossil Eozoon 

 Canadense, which is referred to this order, was of indefi- 

 nite size. The Foraminifera accumulate in the bed of 

 the ocean in great numbers, yet in former ages they 

 were still more prolific, since the Chalk cliffs of England. 



