230 RECENT RESEARCHES IN THE DIATOMACEX. 
want of symmetry in the axis of separation, and the Cymbellee in the 
longitudinal axis, the Gomphonemee are un etrical in the 
transverse axis. The two last-named groups are more closely related 
than has been hitherto believed both in respect to the structure of 
their valves and also of their cell-contents. On the one side the 
Besides, the median lines at the central nodule and the under end- 
nodule bend towards the same side—namely, that in which the above- 
Sart is ne occur, and which are situated in a well-defined 
area, t 
metrical Gomphonemee (e.g., i Sphenella vulgaris) the less 
convex girdle-band, The central plasm-mass ot so broad on 
the one side as it is on the other, on w lie the cell-kernel 
roceeds by an incision from the ends. The free edge grows across 
the valve until the original position has been reached. A transverse 
section of the Gomphonema cell would more clearly represent the 
relative position of the parts. 
ra Gomphonema and Sphenella are distinguished from one 
another only by the circumstance that the frustules in the former are 
stipitate, and non-stipitate in the latter, which Pfitzer, following 
Grunow and Rabenhorst, considers an inadequate generic distinction 
