As author of a flora that should serve diatomists, not only in Europe, as the taxonomic basis of their biological work, one is presented with the following problem when preparing a revision. It should not only reflect the current status of scientific research, but also be so didactically structured, that even biologists without a taxonomic background can work easily with it.
The disparate demands of these goals are very difficult to balanc e, and the authors must decide where compromises must be made.

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In sexual organisms, such as most diatoms, the variation pattern generally lacks a welldeveloped hierarchical structure below a certain critical level, which is where species boundaries should be drawn. Genera and other higher taxa should never be polyphyletic; ranking is never absolute but relative. Infraspecific taxa should generally be avoided until our knowledge of nature, origin and maintenance of the variation pattern has improved significantly.

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The type slide of Eunotia nymanniana Grun. was observed. On the basis of this observation, E. nymanniana collected from Japan was examined in detail. The fine structures of this species and Eunotia compacta (Hust. ) Mayama nov. stat. were described. They are clearly distinguished by means of the areolae density in addition to the valve shape.

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The investigation was carried out on one sample from Kirishima Heights, southern Japan. The epilithic diatoms were collected and the Gomphonema christensenii and Gomphonema clevei were flourishing. Light photomicrograph of almost 200 valves of G. christensenii were analyzed. The form of the valves and the forms of the axial and central areas were similar to the original description by Lowe & Kosiolek, though we observed only few apiculate types in our specimens. Regarding the striae at the central area, the arrangement of the striae was not necessarily perpendicular to the raphe in our specimens and thus differs from the original description. The valve length, breadth and the density of striae in 10 μm were mostly coincident with the original description.

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Approximately 380 valves of Fragilaria capucina var. gracilis were identified on the light photomicrographs from a sample collected from the small pool along Daiya-gawa River. The valves with capitate ends were rare and the margins of the valves gradually narrowed in many specimens (about 91%) from the center to the ends of the valve. According to the original illustration by Oestrup, the breadth of an axial area was wide, while it was narrower in our specimens (about 84%). The central area of our specimens were weakly developed in many valves (62%). The valve morphology of our specimens resembled the illustration of F. capucina var. gracilis by Hustedt (1950) more than the original illustration of F. gracilis var. gracilis by Oestrup (1910). In addition, the microphotographs of F. gracilis Oestrup, Lectotypes Coll. Oestrup 1342 (Tafel 110 Figs 9-11) by Krammer & Lange-Bertalot (1991) closely resembled the valve morphology of our specimens as well as the breadth of the valve.

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Five new genera are described from observations by SEM and they are all monotypic: (1)Streptommion torsivum represents a linear, twisted araphid with occelli of different sizes on each apical mantle; (2) Sagittula transversaria is also an araphid like Eunotogramma, carrying on the ventral mantle a distinctive wall organelle similar to a rimoportula; (3) Gyropandorus annulatus involves a naviculoid having the axial raphe reduced within the panduriform hoop of alveolar rows on the valve; (4) Apterosoma translucida, similar to a Plagiotropis in gross morphology, is characterized by a canal raphe system which lacks fibulae and helictoglossae; finally (5) Eupterotrum pulcherum bears a close resemblance to Entornoneis but differs in the framework of alar canal and by having the elaborate girdle bands.
Rimobulla is explained in detail as a new organelle within the mantle wall and is compared to the rimoportula.

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Necessary sample sizes for floristic studies of diatom are discussed. Three samples of epilithic diatom communities collected from different rivers were used to decide the necessary sample sizes. From each sample,14400 frustules were counted. The species-individuals relationship of each sample was approximated to five models: Fisher's logarithmic series model, MacArthur's broken stick model, Brian's negative binomial series model, Preston's logarithmic series model and Preston's canonical lognormal model. The general lognormal model fitted best for all samples. Even after 14400 counts, the presence of taxa that did not occur in each sample was supposed, because the fitted lognormal curve is apparently truncated. Then we attempted two methods for estimating the total number of taxa from smaller samples, i. e., fitting general lognormal model and Morisita's method. It was estimated that only one-third or less taxa in the whole community occurred when the sample size was 400. Usually the total number of taxa estimated by using both methods became underestimate as the sample size decreased. It was probably caused by the concentration of each species on the permanent slide.

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Changes in the species composition in diatom assemblage with recovery of water quality were studied by long-term (1973-1993) monitoring of periphytic diatom in a small river flowing through an urban area. When the cover by sewer services was low and the water was polluted organically, pollution-tolerant species occurred abundantly in mid-region assemblages. The recovery in water quality was reflected in the decrease of Nitzschia palea and Navicula seminulum, which are regarded to be the most tolerant species. The assemblage composition changed to ones dominated by other tolerant species such as Nitzschia amphibia, Navicula gregaria and Synedra ulna. Subsequently, when the spread of sewer services was over 95% and the recovery of water quality in winter was clear, that decreased to BOD₅ 6 mg.l^-1, N H₄-N 0.64 mg.l^-1a nd PO₄ - P 0.01 mg l^-1, s ensitive species which were observed on the headwater region spread and the diversity increased in mid-region assemblages. However, a change in the species composition in assemblage with the increase of sensitive species, typically Nitzschia dissipata and Rhoicosphenia abbreviata, was observed later. In these assemblages a high abundance of the species indicating the eutrophic condition was the same as before, but increasingly the indicator species for the mesotrophic condition characterized the diatom assemblages.

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The present paper briefly reviewed the approaches of the studies that concern the evaluation of river water pollution using diatom assemblages. These approaches are: biotic indices, multivariate analyses, diversity indices and species-abundance analyses. The merits and limitations of each approach were then discussed.

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A floristic study of epiphytic and epilithic diatoms of Kakita-gawa (Kakita River) springs, Shizuoka Prefecture, was carried out. Diatoms were examined using light microscope (LM) and electron microscopes (SEM and TEM). A total 62 taxa, belonging to 20 genera were found from this area. These taxa include Amphora ovalis Kiitz. that is new occurence in Japan, and A. liriope sp. nov. (nom. nud. ). Dominant taxa in the area were Achnanthes lanceolata, Diatoma mesodon, Melosira variance, Nitzschia dissipata, Navicula joubaudii and N. veneta.

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The diatom flora and some environmental conditions of diatom habitats were studied in Kushiro mire, Hokkaido, Japan. Sampling sites were located in various types of higher plant vegetation (i. e. alder swamp, sedge fen, reed fen and sphagnum bog). Water temperatures varied little among sampling sites. The water in sphagnum bog had much lower pH values. DO (dissolved oxygen) varied from site to site. There were some sampling sites in sedge fen and alder swamp that were more shaded than those in other higher plant vegetation. A total of 121 species of diatoms were collected from these sampling sites. They were mainly benthic diatoms. The numbers of species collected at each sampling site were from 13 to 45 species. Smaller numbers of species were collected in sphagnum bog than in other higher plant vegetation. This may be due to lower pH values of waters in sphagnum bog. From the dendrogram of the cluster analysis, on the whole, diatom communities that were observed in the same type of higher plant vegetation were classified into similar groups.

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Diatom assemblages from the Kurozo-moor were investigated. The moor was developed in a valley, and was scattered with Sphagnum bogs. Samples were collected from ponds, bogs, fallow paddy fields, and a river in the moor in September 1994, March 1995 and August 1995. As the result of taxonomic studies of these sample,105 taxa belonging to 27 genera were identified. Aulacoseira subarctica, A. laevissima, Eunotia curvata, Frustulia rhomboides, Rhopalodia acuminata, and Tabellaria flocculosa were abundant in the moor. A large number of taxa belonging to the genera Navicula and Pinnularia was also found, though most of them were not abundant. Diatom assemblages in the river were quite different from the others.

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The water quality of 21 springs in Kanazawa City and its suburbs was surveyed from 1992 to 1996, using diatom assemblages as environmental index, supplemented by measurement of some physicochemical variables.
DAIpo values ranged from 50 to 89, indicating that the degree of water pollution at all sites corresponded to the oligosaprobic level in the former sapobic system. There was a significance between DAIpo and EC values. All the springs in this study were classified into 3 types according to geographical features and then into 7 types with reference to DAIpo values
I. Mountainous regions: (1) Springs with clean water quality (DAIpo 60-89) in Morimoto mountainous region (Nos.1-3, No.14) and Utatsu-yama mountainous region (No.7); (2) Springs with somewhat worse water quality( DAIpo 55-56) in Utatsu-yamam ountainousr egion (Nos.4 -6).
II. Plateaus; (3) Springs with clean water quality( DAIpo 61-69) in Kodachino plateau (Nos.8,9 ); (4)Springs with somewhat worse water quality( DAIpo 53-60) in Kodachino plateau (Nos.10-12) and Teramachi plateau (No.13).
III. Alluvial fans and lowl ands; (5) Springs with clean water quality (DAlpo 60-82) in Tedorigawa alluvial f an ( Nos.18-21); (6) Spring with somewhat worse water quality( DAIpo 50,51) in Kanazawa lowlands (No.15) aud Tedori alluvial f an (No.17); (7) Spring with clean water quality( DAIpo 73) in Awagasaki dune (No.16).
Some springs described in (2), (4) and (6) with DAIpo values of 50-54 seemed to have been affected by domestric drainage. They also showed high EC values.

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Succession of marine epiphytic diatoms were studied at Nou town, Niigata Prefecture in Japan. The samples collected from two sites on the concrete of a laver farm and one rock of costal leef about two meters offshore in each winter of 1995,1996 and 1997. The results are as follows.
(1) The 34 genera,64 species,4 varieties and 1 forma of diatoms were revealed at two sites.
(2) The succession of diatom assemblages were remarkably changed every month in winter. It may be different according to the epiphytic materials, ie on the concrete of laver farm and the sma ll seaweeds in winter.

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This paper is an attempt to gain insight into the environmental changes of Lake Hamana, a semienclosed brackish lagoon, central Japan, over the last six thousands years. The following environmental changes were revealed by the study of the diatom remains of two undisturbed cores at the central portion of Lake Hamana.
Lake Hamana was a brac kish lake that had large inputs of marine water about 6000 years ago. The salinity of this time was above 20 ‰ that was similar to the present level. The salinity decreased lower than 10 ‰ from about 4500 years ago, and Lake Hamana became a freshwater lake at about 3000 years ago. A series of environmental oscillations with 700 - 1200 years intervals between fresh and brackish episodes followed till about 500 years ago (1498AD), as shown by alternation of freshwater planktonic forms of Aulacoseira granulata and Aulacoseira ambigua with the brackish water planktonic form of Cyclotella caspia. A sudden increase in salinity after the Meiou Earthquake and the following tsunami (1498AD) caused an abrupt change of diatom assemblages of the lake.

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Diatom assemblages in sediments were analyzed to clarify sedimentary environments during the mid- to late-Holocene and to determine the upper limit of marine facies at the Mokoto site along the Okhotsk Sea in Hokkaido.
There was a replacement of marine and brackish-water diatoms by freshwater ones at +1.80 m altitude. Marine and brackish-water diatoms occurred over 40 % at the horizons below +1.80 m altitude, where a marine diatom Cocconeis scutellum and brackish-water diatoms Bacillaria paradoxa, Navicula peregrina and Synedra tabulata occurred. This indicates that sedimentation took place under a lagoon-like environment. Peat accumulation and the dominance of freshwater epiphytic diatoms indicate peat moor environments at the horizons above +1.80 m altitude. At about 5,500 yrs BP, the Mokoto site changed from lagoon littoral to peat moor conditions. Based on the diatom assemblages in sediments, the upper limit of marine facies can be regarded to be +1.80 m altitude, indicating the mid-Holocene sea-level high stand at the Mokoto site.

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The diatom thanatocoenoses from the bore-hole samples of the lagoon Hachiro-gata r ecl-aimed land were analysed in this paper. The resulsts are as follows.
(1) Identified taxa were estimated with 106 species,17 varieties and 2 formae of 36 genera.
(2) The marine species are dominant in the samples below 41-33m depth. Especially the planktonic species are calculated more than 50 % in this horizon. Also, the brackish water species increases gradually in the middlep art.
(3) The fresh water species are dominant at the uppermost deposit.
(4) The sedimentary environments at the bore-hole site are presumed to be changed from the seawater area to freshwater area through brackish water one toward the uppermost horizon.

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Diatoms in sediments from Lake Aoki, Nagano Pref. (Central Japan) were investigated. Epilithic and benthic diatoms were abundant in the samples but planktonic were rare.
The check-list of 242 taxa includes 117 forms which were n ewly recorded in Lake Aoki. Taxonomically or distributionally noticeable taxa were illustrated.

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A total of 102 taxa, distributed among 25 genera, were recorded in an epilithic sample. The community was predominated by Navicula veneta and significant diatoms were as follows: Cyclotella ocellata, C. orientalis, C. rossii, Cyclostephanos tholiformis, Stephanodiscus aff. vestibulis, Achnanthes alteragracillima, A. flexella, Eunotia aff. botuliformis, Gomphonema hedinii, Navicula schubartii, N wildii, N. aff. novaesiberica, Simonsenia aff. delognei.

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The attached diatom assemblages of mid-Taiwan rivers and their ecological environmental factors were studied during a one year period. Samples were collected each month from eleven sampling stations on six rivers in the middle Taiwan. The species composition, ecological diversity, community similarity, seasonal succession changes and the relationship between diatom communities and water quality were studied. A total of 90 diatom taxa from 19 genera were identified. Only 36 species from 16 genera achieved a relative abundance higher than 5 % in the epipelic and epilithic diatom assemblages. The data from a water quality index (WQI) and a water pollution index (WPI) showed that sampling stations ranged from slight to moderately polluted. However, chlorophyll a content of the dark brown algal community revealed a very weak correlation with the WPI and WQI. Both of the indices were easily disturbed by suspended solid. Vollenweider five-class trophic state classification by means of total phosphorus and inorganic, nitrogen, revealed that most sampling stations were polytrophic. The results emphasized that the abundance of attached diatom assemblages in the sampling rivers derived from high nutrient loading and different diatoms could be dominant during seasonal succession. Moreover, it is possible by observing some abundant, attached diatoms to detect the river pollutant loading.

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