The leptocephalous larvae of the eel family Xenocongridae in the western North Atlantic Ocean are identified and characterized. They are shown to form a compact and relatively uniform group. Larvae of six of the seven known western Atlantic species were found. Chilorhinus suensoni
and Kaupichthys hyoproroides were common, while Kaupichthys nuchalis, Chlopsis bicolor, Robinsia catherinae, and Catesbya pseudomuraena were rarer. No leptocephali of Chlopsis dentatus were found. Although other authors have placed Chilorhinus
as a separate family, the morphology of the larva suggests that it is a typical xenocongrid, and it is so treated. Leptocephalus hyoproroides Strömman is shown to be the larva of Kaupichthys diodontus (including K. atlanticus), and is accepted as the valid name of
the species. The nomenclatural problem raised by the priority of names based on leptocephali is discussed. Keys to the xenocongrid eels of the western North Atlantic, both larvae and adults, are given. Station data and counts and measurements are given for all specimens, and each species is
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