In the neighbourhood of Gromia we may, perhaps, place the singular marine Rhizopods which Sir Wyville Thomson has raised to the rank of a distinct order under the name of Challengerida, from the type-genus Challen-geria. This group comprises minute Rhizopods enclosed in a monothalamous test of silica, the form of which varies, being globular, lenticular, flask-shaped, or triangular. The surface of the shell is usually sculptured, often with deeply sunk pits, and there is a single pseudopodial aperture, "usually guarded by a beautifully-formed and frequently highly-ornamented lip" - ('The Atlantic,' vol. ii. p. 341). The sarcode in the interior of the test is granular, with one or more nuclei, and with a number of brown or nearly black, compound, granular bodies.