PROC. BIOL. SOC. WASH. 99(2), 1986, pp. 335-346 NEMATOCHARAX VENUSTUS, A NEW GENUS AND SPECIES OF FISH FROM THE RIO JEQUITINHONHA, MINAS GERAIS, BRAZIL (TELEOSTEI: CHARACIDAE) Stanley H. Weitzman, Naercio A. Menezes, and Heraldo A. Britski Abstract. —Nematocharax venustus, a new genus and species, is described from the lower portion of the Rio Jequitinhonha in Minas Gerais, Brazil. The adult male of this species is distinguished from all known characins by the combination of elongate, filamentous dorsal, anal, and pelvic fins, and a nearly full series of maxillary teeth. The possible relationships of the new genus are briefly discussed but no corroborated hypothesis of relationship is advanced. The status of the knowledge of the fish fauna of the Atlantic forest of eastern Brazil is briefly discussed. The description given below of a new species of characid from the Rio Jequitinho-nha is a small contribution towards increas-ing the data base for studies of the biogeog-raphy of the small and modest-sized littoral streams of eastern and southeastern Brazil. Although the characid fish described herein is probably quite common in at least the middle and lower course of the Rio Jequi-tinhonha it apparently has been collected only twice, first in 1966 from the Rio Je-quitinhonha at Itaobim, Minas Gerais and again in 1985 further east in the same river near Salto da Divisa. It was very common at both collecting sites. That a relatively common, distinctive, easy-to-capture fish of eastern Brazil is now being made known to science is a fact representative of our poor knowledge of the fish fauna of the region. Much future descriptive, phylogenetic, and faunal research must be published before adequate biogeographical studies of this re-gion's fishes can be accomplished. Methods and materials. —Counts and measurements are those described by Fink and Weitzman (1974:1-2). All measure-ments other than standard length (SL) are expressed as a percentage of SL except sub-units of the head which are expressed as a percentage of head length. Ranges and means of the meristics and morphometries are giv-en in the tables, with information for the holotype given separately. Ranges and means for counts in the tables are repre-sented by one set of figures for both sexes combined except in cases of obvious sexual dimorphism where the information is given by sex. Logarithmic and square root trans-formed data were used in covariance anal-yses of sexual differences in measurements and counts respectively. Specimens examined for this study are deposited in the Museu de Zoologia da Uni-versidade de Sao Paulo (MZUSP), the Na-tional Museum of Natural History, Smith-sonian Institution (USNM), Museum of Zoology, University of Michigan (UMMZ), the Academy of Natural Sciences of Phila-delphia (ANSP), the British Museum (Nat-ural History) (BMNH), Field Museum of Natural History (FMNH), and the Museu Nacional de Rio de Janeiro (MNRJ). Nematocharax, new genus Type species.— Nematocharax venustus, new species. Diagnosis.— A "tetragonopterine" char-acid distinguished from all other genera of American and African characids by having a combination of elongate branched dorsal-.