Differentiating diatom groups, which were proposed for water quality evaluation of Japanese - t ype river (Kobayasi & Mayama 1989), are nomenclaturally revised. New name s were designated for 32 taxa among Group A and Group B taxa. Taxonomic comments are described in some species, including a new combination, Craticula molestiformis (Hustedt)Mayama.

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An attachment mode of diatom valves is reported through SEM observations on frustules derived from the Miocene Nabuto Formation. All the frustules examined, which are of centric type either cylindrical or biconvex and consist of two thick-walled valves, and the attachment is completed by abutting their truncated or flanged edges on each other without intercalations between them.
Various types of frustules t h at share this particular mode of attachment have been observed in eleven new taxa (including two new combinations) described under five new genera: Eustephanias, close to Stephanopyxis Ehr., has three concentric rings of rimo portules combined with or without pericentral locking processes. E. rami genus, E. quasinermus and E. inermis are included; Biturricula, monotypic with B. unca, raised a lofty pro cess at the valvar apex to interlock; Dactylacanthis with three new species (D. rara, D. Proxima and D. invalida) forms chains of frustules by tangling their slender processes. In Stephanonycites, to which Sn. variegatus, Sn. coronus and Sn. tabularis belong, the marginal locking spines are hollow and complex but free from rimoportules, unlike the above; and Stictolecanon has a skeletal frame of valves similar to that of Stictodiscus Grey. but develops a deep valve mantle and central rimoportules in the case of Sl. papillatum and Si. geminum.
All but Stictolecanon are grouped into a new family Eustephaniaceae due to their sharing common features: the unique valve attachment by flanged edges, the thick silicified valves with the loculate areolae, the interlinking system and the concentric allocation of the rimoportules.

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Four new genera are described with seven new species and two new combinations within a newly established family, Parodontellaceae, from the early Miocene Nabuto Formation in central Japan. The genera share several common features among barrel-shaped or cylindrical frustules, the main feature being that the loculate valves ofGyrosigma/Pleurosigma type are truncated into a plain valve face, which is thus naturally differentiated, without relying upon the marginal ridges, from the slanting valve mantle of great depth. Three are ocellate while the other is not.
Thamnodiscus is monotypic with T rectispinosus typified, which has truncated-conical valves devoid of ocellar projections but instead with paired processes occluded by the internal rimoportules around the valvar centre. Stylorium (S. truncatum and S. alticolle included)is defined as sessile-eyed with two isolated ocelli near the mantle edge of the circular valve. Parodontella, composed of four species- P. calamus (=Biddulphia calamus Temp. & Brun), P. paucispinosa, P. obliqua and P. clavifera, is stalk-eyed on the lanceolate valve face which has the topmost ocelli of the tubular elevations. Finally, Acigonium with A. gladarmatum and A. gladiorum (=Biddulphia gladiorum Mann) incorporated bears two apical ocelli at the proximal corners of the narrow valve mantle and sword-shaped marginal processes associated with rimoportules. In the first two genera the areolae stretch in biparabolic lines from a central reticulum on the valve face, while in the rest they are in bilateral rows around the axial sternum. Morphologic features that relate the genera to one another are discussed to help coalesce them into one family.

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This study was carried out on an epilithic sample obtained from a stretch of river, dozens of miles up from the Fair River estuary in North Carolina, USA. Light microphotographs of 275 valves of Navicula tenelloides Hustedt were analyzed. Generally, the overall form of these valves were lanceolate (69.0%) with acute ends (70.5%) and small central area (87.1%). Such morphological variability is not shown in either the original description by Hustedt (1937) or the holotype's photo by Simonsen (1987). However, we identified our specimens as Navicula tenelloides, because some specimens from this single assemblage shared several other characteristics with Hustedt's specimen, namely size (length and breadth), density of striae, degree of protrusion at the ends of the valve, shape of the central area and striae arrangement.

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Matsukawaura Lagoon in Fukushima Prefecture is known to be a brackish-water lagoon with a small entrance to the Pacific Ocean. Diatoms from superficial oozes from the bottom of this lagoon have been reported by Kosuge (1972). Since then, the lagoon has been dredged and shore protection constructed with concrete. In 1998 we investigated this lagoon again and analyzed the diatom assemblages.
In this paper we have attempted to com pare the diatom assemblages and water environments of the two investgations (1966 and 1998). The results are as follows:
(1) The taxa found in this area belong to 52 genera and comprise 136 species,13 varieties and 1 forma.
(2) In 1966 the lagoon was composed of seawater, polyhaline-water and mesohaline-water, but in 1998 it had changed to mostly seawater and narrow polyhaline-w ater.
(3) Of the diatom assemblages, freshwater and freshwater- oligohaline species show a decrease of 10-20%, whilst marine and marinepolyhaline species have remarkably in creased since 1966.
(4) Small crustaceans that had inhabited the tidal sand beach disappeared because of dredging and of the construction of the concrete sea bank.

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Diatom flora and some environmental conditions of their habitat were studied at a salt marsh in Vladimorovo, Sakhalin, Russian Federation. The sampling point was covered by Phragmites communis, Carex spp. and some beach or wetland species of spermatophytes (e. g., Potentilla egedei v. groenlandica, Lathyrus palustris v. pilosus). The depth of water was ca.15 cm and salinity was 1.2% (pH=7.2). A total of 48 species were collected, which were mainly benthic diatoms. Although many species occurred were brackish forms (e. g.,Rhopalodia brevissonii, some species of Tryblionella), freshwater (e. g., Amphora veneta)or marine (e. g., Navicula crucicula) forms were also observed. The salinity of the water may change according to the tide level. Diatom flora of this salt marsh was unique. The species composition of diatom assemblage was compared with those found in habitats supporting spermatophytes (i. e., alder swamp, sedge fen, reed fen, sphagnum bog) within the Kushiro mire, which is a typical northern wetland on the Pacific coast of Hokkaido, Japan. The proportions of diatom taxa common to this marsh and Kushiro mire to the all taxa occurred in this marsh were generally low (2.1-12.5%).

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The water quality of the springs in Noto Peninsula was surveyed from 1994 to 1997, through the use of DAIpo (Diatom Assemblage Index to organic water pollution), supplemented by some physicochemical variables.
DAIpo values obtained from t he attached diatom assemblages at the sampling sites, ranged from 60 to 99. These values indicate that the degree of water pollution at all sites corresponds to the oligosaprobic level in the former saprobic system. The springs in this study can be classified one of the following 3 types:
1. The springs with a water quality at the xenosaprobic level (DAIpo 88-99), include those springs (Nos,8,9,13,14,15) distributed from Uchiura Town to Yanagida Village and Monzen Town at the headpoint of this Peninslula.
2. The springs with a water quality at the δ-oligosaprobic level (DAlpo 74-84), include those springs (Nos.1,3,4,6,10,17,18).
3. The springs with a water quality at the α-oligosaprobic (DAIpo 60-68), include those springs (Nos.2,5,7,11,12,16,19,20) scattered all over the densely populated zone and its vicinity or around tourist resorts.

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Fossil diatoms were found from the Morito and Abuzuru Formations of the lower part of the Hayama Group in Miura Peninsula, central Japan. The presence of Crucidenticula sawamurae, Delphineis kamenooensis and Medialia splendida s.1. and the absence of Crucidenticula kanayae suggest that the age of all sample horizons of the two formations ranges from 17.8 to 16.9 Ma (the upper part of the Early Miocene C. sawamurae Zone). This age is much younger than that of the basal part of the Hota Group in Boso Peninsula, central Japan.

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Diatoms are the most abundant of all aquatic living things in the hydrosphere; they are adapted to various environments and have high diversity. Here I present environmental changes in pre-historical to historical ages based on the analyses of diatom fossils from 48 archaeological sites in Japan.
I noted indicative characteri s tics of fossil diatoms, and collected them at the following sites: Tomizawa site (Sendai City of Miyagi Prefecture, Paleolithic to Kofun Periods), Matsukawado site group (Kasugai City of Aichi Pref., middle Jomon to Edo Periods), Asahi site (Kiyosu-cho and three towns of Aichi Pref., middle Jomon to Medieval Periods) and Okajima site (Nishio city of Aichi Pref., final Jomon to Medieval Periods).
In the deposits of the Paleolithic Period, I found numerous d iatoms and many insect fossils at the Tomizawa site. I reconstructed a paleogeographical map based on the appearance rate of aquatic diatoms and terrestrial diatoms. Each diatom can be separated into those that inhabited slightly above or below the ground at that time. This indicates that diatom and insect fossils did not move their living position.
Boring core samples of the early part of the Jomon Period at the Okajima and Asahi sites, include diatom fossils, mostly belonging to the inner bay or coastal diatoms, such as Cyclotella striata, Thalassionema nitzschioides, Thalassiosira spp., and Paralia sulcata Therefore during postglacial transgression, the coastal plain submerged rapidly in the early Holocene, and its coastline invaded towards the central parts of the Mikawa and Nobi Plains.
The deposits which contained a lot of brackish and marine diatoms in the late Jomon Period were found in the low land sites facing the coastal plain (Second marine transgression in the late Jomon Period). And when the Akahoya (6,300yrsBP) and the Matsukawado (3,120 ± 120yrsBP) volcanic ash layers fell, water conditions based on diatom analyses suggested a remarkable change in the water ecosystems.
Big changes of flora and fauna in the Yayoi Period are also indicated by the prolific occurrence of the paddy field diatoms and insects when the water supply system was developed nationwide for the paddy agriculture. Standardization of living things in the lowland was caused by rice cultivation in Japan. As a result of human impact on the natural ecosystem, distinct changes in the biological community occurred. From the Yayoi to Kofun Periods, saprophilous diatoms, eutrophic diatoms, coprophagous insects, saprophagous insects and parasite eggs were found from the Asahi and some other sites. These urban living things indicate the possibility of the existence of breeding animals and the concentration of people in the Asahi moated circular settlements. With the development of an agricultural society, ecological changes and environmental pollution seem to have been accelerated.
In the historical age, I found epiphytic diatoms on seaweeds in the fragments of the salt-making pottery, which educed a method of the ancient salt-making. In addition, I investigated fossil diatom assemblages in Medieval moat deposits of the Kiyosu-jokamachi site at Kiyosu town in Aichi Prefecture, which clearly showed the paleoenvironmental transition of the site.

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Diatom assemblage in the sediment of Lake Nojiri was examined. A total of 245 taxa among 42 genera were recorded. All taxa, which occurred abundantly, were planktonic species, i. e. Fragilaria fasciculata, F crotonensis, Asterionella Formosa, Cyclotella radiosa, C. stelligera, Aulacoseira itarica.

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The attached diatoms in the sample t aken from the marsh of Alewa Heigts Spring in the south of Oahu Island, Hawaii on 26 November 1998 were investigated.
A total of 26 taxa; 21 species,4 varieties and 1 unidentified taxa, belongingto 15 genera were found in the sample.
Dominant taxa in the sample were Achnanthes lanceolata, Cocconeis scutellumvar. parva, Eunotia lunaris, Furstulia rhomboides var. crassinervia, Surirella angusta and Terpsinoë musica.

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