94: MICROSCOPY FOR BEGINNERS. 



f. Valve not curved nor S-shaped (g). 



f. Valve in side view arched, the convex edges scal- 

 loped. Eunotia, 11. 



f. Valve long S-shaped. Pleurosigma, 12. 



f. Valve boat -shaped, the ribs conspicuous. Suri- 

 rella, 13. 



f. Valve boat-shaped, ribs none. Namcula, 14. 



g. Valve strongly ribbed ; a nodule at each end and 



in the centre. Pinnularia, 15. 

 g. Valve not ribbed ; with a central longitudinal, and 

 , a transverse smooth band. Stauroneis, 16. 



1. MEKIDIOK CIECULARE (Fig. 62). 



Valves wedge - shaped, transverse lines indistinct, 

 bands spiral, often broken into small curved sections 

 (Fig. 62). 



Fig. 62. Meridion circulare. Fig. 63.-Diatoma vnlgare. 



2. DlATOMA VTJLGARE (Fig. 63). 



Frustules oblong, the four angles right-angles, band 

 often attached to aquatic plants, easily separable into 

 its component frustules (Fig. 63). 



3. BACILLAKIA (Fig. 64). 

 Frustules long and narrow, united laterally,; freely 



