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Fishes of the family Atherinidae, known as silversides, inhabit marine, brackish and freshwater environments in the Americas. Except for three species, American silversides have been assigned to two indigenous subfamilies--the Atherinopsinae and the Menidiinae, to which the term New World silversides is applied. The exceptions, Atherinomorus stipes, Allanetta harringtonensis and Alepidomus evermanni, belong to the Old World subfamily Atherininae. Comparative morphological studies lead to the inference that New World silversides have shared a common evolutionary history with respect to all other atherinids. This inference is based upon 11 characters that are unique within the family. Furthermore, five derived characters were discovered that support the monophyly of the Atherinopsinae, and nine for the monophyly of the Menidiinae. The compositions of these subfamilies are almost identical to those recognized by Schultz. The Menidiinae comprise such genera as Menidia, Chirostoma, Melaniris, Membras and Coleotropis. A phylogenetic analysis shows that the subfamily contains two major lineages that I recognize as tribes. The first tribe contains the genera Menidia, Chirostoma, Poblana and Labidesthes. The second tribe contains 13 currently recognized genera: Membras, Adenops, Hubbesia, Xenomelaniris, Atherinella, Melaniris, Xenatherina, Archomenidia, Coleotropis, Eurystole, Nectarges, Melanorhinus, and Notocheirus. Phylogenetic analyses, both Wagner and Compatibility, for almost all species of the latter tribe showed a basal bifurcation of a lineage containing Membras, Hubbesia and Adenops and another containing all remaining taxa but Melanorhinus. The species of Melaniris were found to grade morphologically between other genera rather than forming a monophyletic group. Members of this tribe are reclassified into three genera: Membras, Atherinella and Melanorhinus. The genus Atherinella is the largest of the three, containing 34 species which are subdivided into four subgenera and three species groups. The relationships of A. milleri and A. colombiensis are ambiguous and they are not assigned to any subgenera at present. The systematics of the subgenus Atherinella is presented in detail, with the description of two new species and two new subspecies. The species names pachylepis and guatemalensis were each found to have been applied to more than one species.