Fig. 20.—a, Amœba, a fresh-water naked Rhizopod; and b, Actinophrys, a fresh-water Protozoon of the group Radiolaria, with thread-like pseudopodia.
Fig. 21.—Nonionina, a modern marine Foraminifer. Showing its chambered shell and netted pseudopodia.—After Carpenter.
If we attempt to trace the Rhizopods onward from the Middle Laurentian, we are met with a great hiatus in the Upper Laurentian. The species Eozoon Bavaricum has, however, been found in rocks apparently of Huronian age; but this is the last known appearance of Eozoon, properly so-called. In the Cambrian or Siluro-Cambrian, however, we meet with many gigantic Protozoa, more especially those known as Stromatopora, Archæocyathus, Receptaculites, and Cryptozoon.
Fig. 22.—Stromatopora concentrica.—After Hall.