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Show 366 MR. R. I. POCOCK ON TIIE [Apr. 21, P art IV. D istr ibu t io n of some of th e F am il ie s of A rac iin om o r p il e THAT WERE REPRESENTED IN THE O l IGOCENE PERIOD. The only fossil Spiders, with one or two exceptions, of which the generic determination may be trusted, are those that have been found in the amber-beds of Oligocene age. Those that have been referred to genera not now known to exist have no special importance from a geographical standpoint; but of those that have been assigned to existing genera, the following may be taken as a fairly complete list:-Segestria and Dysdera (Dysderidse); Eresus (Eresidse) ; Amaurobius (Dictynidse); Aranea, Zillct, Tetra-gnatha, and Nephila (Argiopidse); Archaza (Archseidae); Tegenaria and Agelena (Agelenidae); Drassus (Drassidae); Clubiona, Any-phcena, and Sparassus (Clubionidse) ; Thomisus and Philodromus (Thomisidae). Although since the Oligocene these Spiders have had the same time for dispersal, they nevertheless differ greatly in their distribution. Dysdera, for example, is apparently indigenous only in the Mediterranean and central portions of Europe and Asia1; Eresus is found in South and Central Europe, Central Asia, China, and Africa to the north and south of the Sahara; Amawrobius all over the world with the exception of India, tropical Africa, and Madagascar; Aranea and Tetragnatha are cosmopolitan; Nephila is mainly restricted to the tropics and the Southern hemisphere, though in Eastern Asia it extends as far north as Japan, and in North America enters the Southern States of the Union ; Archcea is known only from Madagascar; Tegenaria is indigenous apparently only in Europe and North America; Agelena in Europe, South Africa, India, and Burma; Anyphcena in North, Central, and South America (Andes), Japan, India (in the mountains), and Central Europe. The Hersiliidae were represented in the Oligocene of Europe. The four existing genera are distributed as follows:-Hersilia ranges from the southern area of the Mediterranean as far as Malaysia in the Oriental Region, and over Africa and Madagascar. Its very near ally Murricia is confined to India; Hersiliola is known only from the Mediterranean Region and S. Africa. Tama, next to Hersiliola the most primitive of all the genera, occurs in the Mediterranean, Oriental, Australian, and Neotropical Regions. The distribution of the group offers no difficulties to the hypothesis of a southern migration from Europe. The absence of the genus Tama from North and Central America strongly suggests its existence in South America to be attributable to migration from Australia. Two genera of Eresidae have been recorded from the European 1 Specimens that have been recorded from the Southern hemisphere are mostly, probably in all cases, referable to imported European species. |