_Neobalæna._[132]—Head about one-fourth the total length. Skin of the throat not plicated. A small falcate dorsal fin. Vertebræ, C 7, D 17, L 3, C 16 = 43. The cervical vertebræ are united. The manus small, narrow, and tetradactylous, wanting the pollex. The ribs remarkably expanded and flattened. The scapula very low and broad, with completely developed acromion and coracoid processes. Tympanic approximating to that of _Balæna_, but with certain very characteristic peculiarities of shape. Baleen very long, slender, elastic, and white. A single species, at present very rare, _N. marginata_, from the Australian and New Zealand seas is the smallest of the Whalebone Whales, being not more than 20 feet in length. _Rhachianectes._[133]—This combines the small head, elongated form, and narrow pectoral fin of _Balænoptera_ with the smooth skin of the throat and absence of the dorsal fin of _Balæna_. The baleen is the shortest and coarsest of any of the group. Its osteology is imperfectly known. One species, _R. glaucus_, the Gray Whale of the North Pacific. _Megaptera._[134]—Head of moderate size. Baleen plates short and broad. Vertebræ, C 7, D 14, L 11, C 21 = 53. Cervical vertebræ free. Scapula with acromion and coracoid process absent or rudimentary. Skin of throat plicated. Dorsal fin low. Pectoral limb tetradactylous, very long and narrow, attaining about one-fourth of the length of the entire animal, the metacarpus and phalanges being greatly developed, and the latter very numerous. Tympanic still more inflated than in _Balænoptera_, with the involuted portion more distinctly pyriform, the Eustachian part of the aperture well defined, and two well-marked longitudinal ridges on the lower surface of adult specimens.