SPHENODERIA DENTATA. 65 



The dentate chitinous border of the aperture (fig. 

 138) is similar to that of Assulina ; it is very thin, 

 transparent, and colourless, and its outlines are often 

 difficult to distinguish ; rarely individuals are found 

 in which it is absent. 



FIG. 136. Oval scales of Sphenoderia dentafa. x 1000. 



The test resembles that of EuglypJia alveolata, but 

 is easily distinguished by the character of the aperture. 

 The test may vary in diameter from half to two thirds 

 of its length, but always retains its circular trans- 

 verse section ; it is usually very constant in its form 



ooOOOOO 



Fia. 137. Various types of scales of Spenoderia dentata. x 1000. 



and general appearance. The scales when oval are 

 usually a fifth to a sixth of the length of the test; 

 when they are circular their diameter may vary from 

 a sixth to a tenth of that. The nucleus may contain 

 a single nucleole or have a granular central portion. 

 It is one of the species which are characteristic of 

 the drier mosses. 



FIG. 138. Aperture membrane of Sphenoderia dentata. x 1000. 



VOL. III. 



