The first contribution in this volume investigates mainly the province of Khentii, covering an area with dominating higher or lower mountain ranghes and tablelands above 600 m.s.l. Thus the diatom flora was supposed to resemble alpine and northern regions of Europe rather than mediterranean - like or subtropical regions, which proved to be correct. The 3487 micrographs reproduced in this book encompass approximately 615 taxa - without any attempt to approach completeness in this first volume of a treatise. 65 taxa (64 from Mongolia) are described as new to science, 33 other taxa will prove probably as new species after some more information, about 114 taxa could not convincing characters to be distinguished from more or less similar taxa. - The second smaller monograph in this volume deals with Sichuania lacustris, a biraphid diatom possessing an unique frustule morphology, completely dissimilar to all established taxa from freshwater habitats.