252 34 
32. Pinnularia sp. tab. nostr., fig. 8. 
L. 0,049 mm., B. 0,01 mm. Striz 10 in 0,01 mm. 
Valve rectilinear with rounded apices. Terminal fissures comma- 
shaped. Apical area narrow. Striz parallel, at right angles to the 
apical axis, absent in the middle, so that a transapical area arises. 
As I have seen but one specimen of this small form, I dare not 
regard it as a distinct species. It seems to be nearest to Pinn. macilenta 
(Ehr.) Cl. 
Amphora Ehr. (1840). Cl. Syn. Il, p. 99. 
33. A. acutiuseula Ktz. V.H. Syn. tab. I, fig. 18. 
Solitary in a sample from Lem Dan. 
Area: Greenland, Spitzbergen, Europe, Madeira, New Zealand, Samoa. 
Achnanthes Cl. Syn. II, p. 163. 
Actinoneis Cl. 1. c. p. 185. 
34, A. oblongella Ost. nov. sp. tab. nostr., fig. 9. 
L. 0,057 mm., B. 0,006 min. 
Epitheca: apical area narrow, 10 striz in 0,01 mm., finely 
transversely lineated. Hypotheca: striae very fine, slightly curved. 
Central area narrow. 
Hypotheca of this small species highly reminds of Navicula 
Rotewana Grun. var, oblongella Grun. (V. H., Syn. tab. XIV, fig. 21). 
But as I have seen both valves in situ, I am quite sure it is an 
Achnaathes. 
Klong Majum. 
In the same sample where Ach. oblongella occurs I found a small 
form, which I have figured in tab. nostr., fig. 10. 
Valve oblong elliptical, L. 0,018 mm., B. 0,007 mm., strize 10 in 
0,01 mm., somewhat shortened so that an apical area arises. In 
specimens mounted in styrax it was impossible to see any raphe, 
but in a dry specimen I could catch a glimpse of a such one with 
distant central pores. As to the structure of the valve all the spe- 
cimens examined were identical. Thus I dare not decide if the 
present form is an Achnanthes or a Navicula. 
Microneis Cl. 1. c. HU, p. 187. 
35. A. minutissima Ktz. V.H. Syn. tab. XXVIII, figs. 37—38. 
Klong Majum, Klong Munsé, Lem Dan. (4 samples). 
var. eryptocephala Grun. V.H. |. c. figs. 41—44. 
Klong Prao, Klong Munsé, Lem Dan. 
Area: the main species: Greenland, Europa, Mongolia. var. eryptocephala 
according to Cleve (I. ¢. p. 188) Finland. I have found it in the Ferd Islands. 
and in Denmark. 
