PROCEEDINGS OF THE -^."^ CALIFORNIA ACADEMY OF SCIENCES Fourth Series Vol. XXIII, No. 8, pp. 99-114. May 28, 1937 No. 8 THE FISHES OF THE BENI-MAMORE AND PARAGUAY BASINS, AND A DISCUSSION OF THE ORIGIN OF THE PARAGUAYAN FAUNA* BY NATHAN E. PEARSON Associate Professor of Zoology Butler University The resemblance of the freshwater fish fauna of the La Plata to that of the Amazon basin has been known since the earliest collec-tions were made in those regions. During the past fifty years the identification of a great amount of material taken from numerous localities in those river systems has further emphasized this simi-larity. Jordan ('96) pointed out that the marshy character of the upland between the Tapajos and the Paraguay would permit the free move-ment of fishes between the two basins. Eigenmann ('06) and Eigen-mann, McAtee, and Ward ('07) directed attention to the low nature of the divide between the Guapore and some of the principal head-waters of the Paraguay and suggested this as a possible migratory route. Haseman ('12) was unable to account for the remarkable simi-larity of the freshwater fish fauna in many of the smaller river basins whose headwaters are near those of the Amazon, by migration of forms now existent in the Amazon, and used the Paraguay and Amazon basins as examples to illustrate the hypothesis of parallel evolution as applied to the South American freshwater fish problem. ♦Printed from the John W. Hendrie Publication Endowment. This paper was filed for publication on June 16, 1930. Through no fault of the author its appearance has been delayed by a series of unforeseen circumstances. May 28, 1937
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