— 29 — 



Neidium Pfitzer (1871), GL Syn. I, p. 67. 



2. N. affine Ehr. var. genuina Gl. forma minor. A. S. Atl. tab. XLIX, 

 fig. 23. 



Lem Dan (7 samples). 



Area: the main species: ubiquitous, f. minor: Spitzbergen, Europe, Au- 

 stralia. 



3. N. Hitchcockii Ehr. A. S. Atl. tab. XLIX, figs. 35-36. 

 Klong Son, Lem Dan (7 samples). 



Usually with oblique striæ, forming an angle of about 75° to the 

 apical axis. 



Area: North America, Europe, Bengal, Australia, New Zealand. 



Frustulia Ag. (1824), GI. Syn. I, p. 121. 



4. i\ rhomboïdes Ehr. V. H. Syn. tab. XVII, figs. 1—2. 



Found in many (20) of the samples. In some of them e. g. from Klong 

 Munsé and Lem Dan not rare. 



var. saxonica Rabh. V. H. 1. c. fig. 4. 



Mixed with the main species. 



Area: the main species and the var. saxonica: America, Europe, Asia, 

 Australia. 



Stauroneis Ehr. (1843); cnfr. GI. Syn. I, p. 141 Namculœ 

 microstigmaticœ. 



5. Stauroneis anceps Ehr. var. hyalin a Br. & Perag. Hérib. Diat. 

 Auv. tab. III, fig. 19. 



Solitary in two samples from Lem Dan and Lem Ngob. 

 Area: Europe (fossil), Australia. 



In a sample from Lem Dan I have found a Stauroneis, in its out- 

 ward form like St. ane. Ehr. var. amphicephala Ktz. (V. H. Syn. tab. IV, 

 fig. 5) but without any visible striation. 



Cymbella Ag. (1830), GI. Syn. I, p. 156. 



6. C. gracilis Rabh. cnfr. A. S. Atl. tab. X, fig. 39; tab. nost, fig. 3. 



Klong Prao, Klong Majum, Klong Munsé, Lem Dan. 



I have figured this form because it differs somewhat from the type 

 by its gibbous ventral margin. 



Area:- Cymb. grac: Greenland, Europe, Tasmania, New Zealand; according 

 to Cleve (1. c. p. 169) especially in alpine regions. 



7. C. japonica Reiclielt. Kunze Rev. III, p. 391. 



Klong Prao, Klong Majum, Klong Munsé, Klong Son, Lem Dan. (7 samples). 

 Area: Japan. 



