PROC. ENTOMOL. SOC. WASH. 95(3), 1993, pp. 383^03 FOSSIL PERISCELIDIDAE (DIPTERA) David A. Grimaldi and Wayne N. Mathis (DAG) Department of Entomology, American Museum of Natural History, New York, New York 10024-5192; (WNM) Department of Entomology, NHB 169, Smithsonian Institution, Washington, D.C. 20560. Abstract.— AW known fossil species of periscelidid flies occur in amber and are treated. Periscelis annectans Sturtevant, from upper Oligocene amber of Chiapas, Mexico, is redescribed and illustrated; it belongs to the subgenus Myodris Lioy. Six new amber species are described, all from the lower Miocene-upper Oligocene amber of the Dominican Republic. Three species are: Periscelis {Myodris): amberifera, brodzinskyi, and fascianota. Other species are: Planinasus electra, Stenomicra anacrostichalis and S. sabroskyi. Keys to some genera and subgenera are presented. Despite their rarity in nature, high diversity of periscelidids in Dominican amber is certainly attributable to an association with de-caying trees. Presence of modem subgenera in the Oligo-Miocene suggests an origin of periscelidids perhaps in the Paleocene. Key Words: Diptera, Periscelididae, Periscelis, Planinasus, Stenomicra, fossil, amber Flies of the family Periscelididae are ob-scure muscomorphans with about 50 de-scribed species worldwide. Specimens are rare in collections notably because their habits are often quite specific to tree trunks and logs that are sometimes in a decaying state (Teskey 1 976). Planinasus Cresson, for example, is frequently found on rotting logs in or near streams in the neotropics, and Periscelis Loew and Stenomicra Coquillett usually occur at sap fluxes of living trees (many neotropical Stenomicra are also found in rolled leaves of Heliconia L., living on beetle frass). Given their predilection for tree trunks and logs, it is not too surprising that an occasional specimen was preserved in am-ber. Five pieces of amber with six specimens of periscelidids represent the total number of these flies seen in about 20,000 pieces of Dominican amber screened by the senior author. Specimens, thus, are quite rare even as fossils in amber. Amber is a generic term for fossilized, highly polymerized, resinous sap that can be exuded from a large variety of coniferous and deciduous trees (Langenheim 1969). Although of varying age, pieces date from the Carboniferous (280-345 million years ago), and those from the Cretaceous (65-140 million years ago) are the oldest pieces with insect inclusions. Because of the fine preservation and three-dimensional detail preserved in amber, it is an exceptional mode of fossilization for small, delicate in-sects like acalyptrate flies (e.g. Baroni-Ur-bani and Graeser 1987, Henwood 1992). The large deposits of Baltic amber (also called succinite) have the longest history of research on their fossiliferous inclusions (Bachofen-Echt 1949). These deposits vary in age from Eocene to middle Miocene (Larsson 1978). Hennig (1965, 1967) re-vised the diverse fauna of acalyptrates in Baltic amber, but no periscelidids are known from that material.
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