Diatoms 



III 



of water moss or a drop of sediment from the bottom 

 without finding Naviculas in the mount. They are 

 more abundant shoreward than in the open waters of 

 the lake. Tlie "white-cross diatom" Staiironeis (d), is a 

 kindred form, easily recognizable by the smooth cross- 

 band which replaces the middle nodule of Navicula. 



Fig. 35. Diatoms. 



a valve view showing middle and end nodules, and b. girdle view of Navicula. c, another 

 species of Navicula; d, Slauroneis: e. valve view and f, girdle view of Tabellaria: g, 

 Synedra; h. Gvrosigma; «, a gelatinous cord-hke cluster of Encyonema showing , girdle 

 view of nine individuals and valve view of three. J. valve view and ft, girdle view of 

 Melosira: I, Stephanodiscus: m, jV/eriiiiore colony, with a single detached individual shown 

 in valve view below; n, a small colony of Asterionella: o. valve view, and p. girdle view 

 of Camplylodiscus: q, cluster of Cocconema. (Figures mostly after WoUe). 



Tabellaria (e and /) is a thin fiat-celled diatom that 

 forms ribbon-like bands, the cells being apposed, valve 

 to valve. Often the ribbons are broken into rectangu- 

 lar blocks of cells which hang together in zig-zag hnes 

 by the corners of the rectangles. The single cell is long- 

 rectangular in girdle view (slightly swollen in the middle 

 and at each end, as shown at e, in valve view), and is 

 traversed by two or more intermediate septa. Tabel- 

 laria abounds in the cool waters of our deeper northern 

 lakes , at all seasons of the year. It is much less common 

 in streams. 



