In 1861, the late Dr. T. C. Winkler, of Haarlem, published a memoir on some fishes from the well-known Upper Miocene fresh-water formation of Oeningen, and among other new forms he believed he could recognize an extinct species of the Cyprinodont genus, Poecilia. This peculiar fish not being known elsewhere beyond the fresh waters of tropical America, the determination of a Miocene representative in a European fresh-water deposit excited some interest both among geologists and ichthyologists; and the occurrence of Poecilia oeningensis in Baden has been almost universally quoted in textbooks and treatises as a fact worthy of special note.

In his memoir Dr. Winkler mentions that he founds the species in. question on a series of specimens, partly in the Teyler Museum, partly in the collection of Van Breda. As the latter collection was acquired by the British Museum in 1871, four of the specimens studied by Winkler are destined to be included in the forthcoming vol. iv of the “Catalogue of Fossil Fishes.” They have thus been recently examined during the preparation of this work; and the result is so completely at variance with Winkler's interpretation of the fossils, that it seems advisable to publish an amended description of the fish without delay.