THE TENUIS GROUP OF LEPTHYPHANTES MENGE (ARANEAE, LINYPHIIDAE) by P. J. VAN HELSDINGEN Rijksmuseum van Natuurlijke Historie, Leiden K. THALER Zoologisches Institut der Universität, Innsbruck and C. DELTSHEV Zoological Institute of the B.A.N., Sofìa With 69 text-figures Introduction Within the Linyphiidae, the genus Lepthyphantes is one of the largest. It is rich in species, which are found in a wide range of habitats, from the Arctic in the north to the Mediterranean in the south, at high altitudes in the Alps as well as in the lower parts of Europe. In Asia, North America, and Africa they occur in comparable situations. A number of species have also been described from other parts of the world, but at least some of these we may regard sceptically. Even with this restriction there is an overwhelming amount of species and the genus is notorious for that very reason. The inaccessibility of the genus is aggravated by the many poor descriptions without, or with inadequate, illustrations. Several authors have tried to arrange the species into natural, monophyletic groups. One of these groups, the tenuis group, will be discussed in this paper. As already pointed out by Wanless (1973: 139), this group is not sharply limited. Notably species as L. alacris (Blackwall) and its near relatives are, at least morphologically, close to the tenuis group, but for practical reasons we have restricted ourselves to the species-group as delimited by Simon (1929, "4e Groupe", p. 589), Locket & Millidge (1953, "Group III", p. 384), and Wiehle (1956, "IV. 7emm-Gruppe", p. 191). We have included as many species as possible which from their descriptions, and above all from the illustrations, could be referred to this species-group. Inevitably some may have escaped attention, because the available descriptions lacked any indication of their belonging to the group dealt with here. Many species of the tenuis group are very common and widely distributed, and every ecologist will collect large series of certain species in his pitfalls or through hand-collecting. Still the identification even of the common species is far from easy, because the palps and epigynes are very small, while the characters l
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