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Contribution to the Knowledge of the Branchiopod and Copepod Fauna of Mongolia One species of Anostraca, 25 species of Cladocera and 19 species of Copepoda are reported, mainly from the eastern Khangai mountains, the Tola valley near Ulan‐Bator, and the Khentei mountains. One subspecies, Arctodiaptomus rectispinosus mongolicus, is new to science. An important fraction of species in the present collection had not yet been recorded from Mongolia. The relations between Daphnia longispina O. F. MÜLLER, 1785 and Daphnia rosea SARS,1862,Simocephalus vetulus (O. F. MÜLLER, 1776) and Simocephalus vetuloides SARS, 1898 are discussed. Due to hydrochemical factors, to trophic and climatic conditions most of the sampled localities can be divided into two groups: those of the mountainous steppe zone with high contents of nutrients and electrolytes and those situated in the northern montainous forest steppe zone which are more or less acidic and poor in nutrients and electrolytes. This is also reflected by the fauna composition.

In the catchment area of Lake Uvs Nuur (Northwest Mongolia) samples of branchiopods and copepods were collected in 15 different lentic water bodies. The waters differ in respect to water chemistry, salt content (fresh, saline), water depth (shallow, deep), catchment area and surrounding landscape and vegetation (semi-desert, steppe areas, alpine regions). 38 species of cladocerans and 16 species of copepods were found. The salt waters (> 0.5 g/l up to 20 g/l) housed altogether 31 species; the fresh waters (< 0.5 g/l) had a distinctly larger number of species (40 species). The populated waters are briefly characterized with regard to morphometry, macrophytes and fish stock. 12 species -8 Cladocera and 4 Copepoda -have not previously been recorded from Mongolia. Morphological and taxonomical remarks are made on certain species.

A new genus and a new species of Canthocamptidae: Maraenobiotus canadensis and Neomaraenobiotus laurentiacus (Copepoda: Harpacticoida) are described and their taxonomic relationships are discussed.

Fr-ossNrn, D., eNo K. Kneus. 1977. On the variability and taxonomy of Pleuroxus denticulatus Birge (Cladocera: Chydoridae). J. Fish. Res. Board Can. 34: 463476.Comparative morphological investigation of extensive series of Pleuroxus denticulttttts Birge from North America and Europe revealed considerable variability in cerlain characters. These are quantitative (body dimensions), qualitative (structure of postabdomen), and meristic (number of ventro-+audal shell denticles). With regard to the postabdomen, two motphotypes, connected by transitional forms, can be distinguished in both sexes, which, however, are not separated geographically. Neverlheless, there are ceftain field populations (e.g. from Indiana and southem Germany) that are so strongly divergent in certain characters they would satisfy the taxonomic requirements for assigning them to different geographic races. The Nofih American population s are distinguished by having significantly more denticles on the ventro-caudal angle of the valves, the frequency distribution of which satisfied the 75% rule for the separation of subspecies. However, we do not consider the distinctness in this single character of a single west European population sufficient to justify the establishment of two geographic subspecies. Trunk limb morphology, which yields important conclusions conceming the systematic afflnities of Pleuro.rus dentitulutLts, is also described. The species, along with Pleurorus truncutus (O. F. Miiller) and P leu roxu s p ro( ut1, us Birge, form a group of closely related species, characterized by the sperm ducts opening on the lateral surfaces ofthe postabdomen and by the relatively small structural differences between the male and female postabdomen. Finally, differentiation of characters within the truncotus group is analyzed in detail.