PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 108(4):662-678. 1995 Gymnotus maculosus, a new species of electric fish (Chordata: Teleostei: Gymnotoidei) from Middle America, with a key to species of Gymnotus James Spurling Albert and Robert Rush Miller Museum of Zoology, University of Michigan, Ann Arbor, Michigan 48109-1079, U.SA. Abstract — A new species of gymnotoid knifefish, Gymnotus maculosus, is described from Pacific drainages of Middle America, from Chiapas, Mexico, to Costa Rica, and an Atlantic drainage in Nicaragua. Morphological, meristic, and pigmentation features are compared with congeners. Variation among the species of Gymnotus from many localities in South America remains to be analyzed for a robust hypothesis about numbers of species and their interre-lationships. A phylogenetic diagnosis of Gymnotus, and a key to the recognized species is provided. Resumen. — Se describe una nueva especie de anguila electrica, Gymnotus maculosus. Esta especie se encuentra en las vertientes Pacificas de Mesoam-erica desde Chiapas, Mexico, hasta Costa Rica, y en una cuenca Atlantica de Nicaragua. Se discuten y comparan caracteristicas morfologicas, meristicas, y de pigmentacion con otros miembros del genero. Para poder establecer el nu-mero de especies de Gymnotus y sus relaciones, es necesario un analisis de la variabilidad entre especies de diversas localidades en Sudamerica. Se provee una diagnosis filogenetica del genero Gymnotus y una clave de identificacion de las especies reconocidas. Gymnotus is the most widely distributed genus of American electric knifefishes (Te-leostei: Gymnotoidei). Members of the ge-nus range from the Rio San Nicolas of southeastern Chiapas, Mexico, south to the Rio de la Plata, Argentina (Eigenmann & Ward 1905, Eigenmann & Fischer 1914, Ei-genmann & Allen 1942, Miller 1966, Buss-ing 1985). Members of this lineage are ag-gressive, nocturnal predators who prefer small tributaries, lagoons, and backwater swamps, and in Middle America sometimes inhabit highland lakes. The systematic position and organization of Gymnotus are problematic. Gymnotus was proposed by Peter Artedi in 1738 to include the type species G. carapo Linnae-us. According to Ellis (1913) the original specimens were collected in the Guy anas. Ellis (1913) was the first to propose a for-mal hypothesis of interrelationships among the major gymnotoid lineages, placing Gymnotus and Electrophorus as the sister lineage to all other gymnotoids (Ellis 1913, Eigenmann & Fischer 1914). Ellis synony-mized all specimens of Gymnotus into the type species, G. carapo. There are presently thirteen described species of Gymnotus, of which five have been synonymized with the type species (Mago-Leccia 1994). Several additional species are recognized in museum collec-tions, however, so that the actual number of species may be substantially higher. De-scriptions of several of these species await the acquisition of sufficient samples from populations across their geographical range (Mago-Leccia 1994). Most specimens of Gymnotus in museum collections are iden-tified as G. carapo, regardless of their ap-pearance or origin. This is due, in part, to the wide geographical extent of this puta-
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