146 JOURNAL OF THE [June, 



view the secondary triangle, with its small, central nodule, is 

 below the focal plane, and no areolation is seen bordering any 

 part of the two blank spaces, resembling openings, which lie 

 between the base of each pseudo-nodule and an apex of the 

 secondary triangle. 



In photograph No. 2 the focus is run in i?f;i;ii7ths of an inch 

 below its position in No. 1. The central nodule is here distinct, 

 and the longitudinal division of its radiating lines can also be 

 seen. The general areolation seems less deep, the convexity is 

 also reduced, and areolation becomes apparent below the base 

 of each pseudo-nodule. 



For photograph No. 3 the focus was run in i7;;;^ths of an 

 inch from No. 2, ori^^i^ths of an inch from No. i. The apices 

 of the secondary triangle, which Dr. Greville represents as plain 

 are here seen to be areolated. The outer border of the diatom 

 is not quite distinct, some convexity still existing. The depth 

 of the entire convexity would seem to be less than ,_oon th of an 

 inch. With the focus lowered about 10,000 ths of an inch further, 

 the convexity disappeared, but no, indication of a row of cells 

 like that shown in Dr. Greville's illustration could be seen. 



