G. Fekete szerk.: Studia Botanica Hungarica 9. 1974 (Budapest, 1974)
Vida, László: Diatoms from a brooklet affluent to Arax river (Armenian Republic, USSR)
59. 60. 61. 62. 63. 64. 65. 66, 67. 68. 69. 70. Nitzschia recta HANTZSCH Nitzschia sigma (KÜTZ.) W. SMITH Nitzschia sigmoidea (EHR. ) W. SMITH Nitzschia thermalis var. minor HILSE Nitzschia tryblionella var. debilis (ARNOTT) A. MAYER Nitzschia tryblionella var. levidensis (W. SMITH) GRUN. Nitzschia vitrea var. salinarum GRUN. Cymatopleura solea (BRÉB.) W. SMITH Surirella angustata KÜTZ. Surirella «ovalis BRÉB . Surirella ovata KÜTZ. Surirella peisonis PANT OC SEK ? II 2M II 21 1H 2H 3M II II 4H 41 1H REMARKS UPON THE TAXA ad 1. Thalassiosira fluviatilis HUST. Fig. 1. HUSTEDT (1926) described this rare and interesting species from the plankton of the rivers Weser and Werra where it had been found in the years 1925 and 1926. No other data ccmcerning occurence of the species is known to me, and it is probable that it has not been reported since from European areas. As for its occurence in the Soviet Union, PROSKTNA-LAVRENKO (1951) makes no report, and SKABICEVSKIJ (1960), although describing the species in details, mentions that it has not been found there so far. PORECKIJ and ANISIMOVA (1933) describe another species, Thalassiosira hustedtii from the Soviet Union. This, being an extremely rare diatom, was found at a single spot, at the mouth of a saline stream near Staraya Russa, district of Novgorod, and was reported inhabiting bottom-mud of very slowly moving waters, coating submerged wood and macrophytes like Enterömorpha. Meanwhile, it could not be found in any of the neighbouring saline waters. Based upon the original diagnoses of the authors, the most important taxonomic marks separating the two species are as follows: Thalassiosira fluviatilis HUSTEDT: Frustules solitary. Valves bearing a few largerpores in the centre, other parts of the shell wall bear extremely delicate pattern of radiate punctae. Density of marginal striae 10-13/lO/i . Diameter 15-23 \i. Thalassiosira hustedtii PORECKIJ et ANISIMOVA: Frustules solitary, rarely forming chains of 2-4 frustules. Valves bearing one larger pore in the centre, with the role of jelly secretion and consequently colony formation. Other parts ot the shell wall plain, structurelles, except a small area round the central pore that bears an irregularly outlined and extremely finely punctated wreath. Density of marginal striae 16/10 p . Diameter 17,2-19, 5 M . Difference between the two species looks significant from the point of theirbiotops. Nevertheless, already SKABIÖEVSKIJ (1960) pointed out that Thalassiosira hustedtii is probably a genuine planktonic diatom like most of the Centricaceae , and thus the benthic-epiphytic occurence in that site should be regarded as secondary.
