Lagenorhynchus
Lagenorhynchus is a genus of Oceanic dolphins in the infraorder Cetacea, presently containing six extant species. However, there is consistent molecular evidence that the genus is polyphyletic and several of the species are likely to be moved to other genera. In addition, the extinct species "Lagenorhynchus harmatuki" is also classified in this genus. Etymology. The name "Lagenorhynchus" derives from the Greek "lagenos" meaning "bottle" and "rhynchus" meaning "beak". Indeed, the "bottle-nose" is a characteristic of this genus. However, the dolphins popularly called bottlenose dolphins belong in the genus "Tursiops". Taxonomy. There is compelling evidence from molecular phylogeny that  the genus "Lagenorhynchus" is polyphyletic, meaning that it currently contains several species that are not closely related. The remaining four species of "Lagenorhynchus": Pacific white-sided dolphin, Peale's dolphin, hourglass dolphin and dusky dolphin consistently appear nested within the Lissodelphininae subfamily in studies of molecular phylogeny, together with the Right whale dolphins and the four species of the genus "Cephalorhynchus" (including Hector's dolphin). Some authors have suggested that these four species are placed in the resurrected genus "Sagmatias". However, other molecular studies recover the hourglass and Peale's dolphins as nested phylogenetically within the four species of "Cephalorhynchus  and thereby speaks against inclusion in a new genus together with Pacific white-sided dolphin and dusky dolphin. This phylogeny is supported by acoustic and morphological data. Both hourglass and Peale's dolphins share with the species of Cephalorhynchus" a distinct type of echolocation signal known as a narrow-band, high-frequency signal. This signal is shared with porpoises (Phocoenidae) and pygmy sperm whales (Kogiidae), but is not found among other dolphin groups. According to , Peale's dolphin and the "Cephalorhynchus" species are the only dolphins that do not whistle. Presumably this is the case for hourglass dolphins, as well . Peale's dolphin also shares with several "Cephalorhynchus" species the possession of a distinct white "armpit" marking behind the pectoral fin. The melon-headed whale was first classified as member of the genus "Lagenorhynchus", but was later moved to its own genus, "Peponocephala".