PLATE I. 



FIG. 28. 



FIG. 27. 



Scale of Hipparchia Janirn. 



Scales of Podura plumbea:&, large 

 strongly marked scale; B, small scale 

 more faintly marked; c, portion of an 

 injured scale, showing the nature of the 

 markings. 



FIG. 29. 



n^r ^r ^ 

 * 



w&w 



Plevrosigma angiilatum : A, entire frustule, as seen 

 under a power of 500 diam. ; B, hexagonal aerolation, 

 as seen under a power of 1300 diam.; c, the same, 

 as seen under a power of 15,000 diam. 



