The beaked whales belonging to the family Ziphiidae are, with the exception of the bottle-nosed whales of the genus Hyperoodon, among the rarest of cetaceans. Of the three genera Mesoplodon, Ziphius, Berardius, so far as ascertained from published records, specimens representing about one hundred individuals are known, and somewhat more than one-half of these belong to the first-named genus. Berardius is the rarest genus, only about fourteen specimens having been collected thus far. The U.S. National Museum contains specimens representing some twenty-five individuals of the three genera, or about one-fourth of the material at present available.