Tetrapturus belone Rafinesque is described on the basis of specimens from the Western North Atlantic. A synonymy is given and the relationships discussed. The species is compared with other Atlantic billfishes and with T. angustirostris of the Indo-Pacific. T. angustirostris
is recorded for the first time from off the Chilean coast. The genus Tetrapturus is redefined, its synonymy given and the constituent species of Istiophoridae realigned according to a proposed phylogeny. A key is given to the species of Istiophoridae exclusive of the sailfishes, Istiophorus.
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