126 AQUATIC MICROSCOPY FOR BEGINNERS. 



2. Shell nearly spherical, with from one to twelve, 



usually from three to seven, pointed spines ar- 

 ranged in a circle around the upper part, and 

 formed of sand-grains. These spines are hollow, 

 and communicate with the cavity of the shell, 

 but the animal probably builds them for orna- 

 ment, asifnever seems to use them- 



The mouth of the shell occupies the end opposite 

 to the spine-bearing summit, and .when the 

 shell is turned over so that this opening is di- 

 rected upward, it will be seen to be lobed or scal- 

 loped, the lobes varying from six to sixteen, be- 

 ing usually about twelve. They may, in some 

 forms, be rather sharp pointed, almost like short 

 teeth, and are in all cases directed towards each 

 other across the opening. It is a difificult matter 

 to get the shell in such a position that the ob- 

 server can look down into its mouth, but this may 

 sometimes be done by tapping the cover-glass 



» with a needle so as to roll the Rhizopod about, and 

 occasionally, by one of those lucky accidents that 

 sometimes occur, it will place itself in good po- 

 sition. 



The soft body is colorless or brownish, and the 

 pseupodia are thick, Dlunt, and numerous. The 

 species is common in the ooze. D. cordna, Fig. 

 98. 



3. Shell spherical, without spines; mouth circular, 



smooth, without lobes or teeth. This species is 

 found with the preceding. D. globuldsa. 



4. Shell long and narrowly pear-shaped, the summit 



prolonged into a central conical projection or 

 sharp point; mouth circular, smooth, without 

 teeth or lobes. Common. D. acumindta. 



