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 they only got driven so closely together after their specific differentiation, when the land gradually subsided, owing to volcanic action. The differentiation of the family is as follows:—

KULL with a short and wide beak. Pectoral girdle very small or absent, wing absent, only an indication in Dinornis dromioides. Hallux absent or present. An extension bridge to the tibio-tarsus, which is placed near the inner border of the bone. No superior notch to the sternum. Most of the species of very large size. The tarso-metatarsus is either long and slender or short and wide, and its anterior surface may or may not be grooved. The second trochlea is longer than the fourth, the third is not pedunculated, and there is no perforation in the groove between the third and fourth trochlea. In the tibio-tarsus the cnemial crest rises well above the head; the extensor groove is separated by a considerable interval from the inner border of the bone. There is a well-defined intercondylar tubercle; the intercondylar gorge is deep, and there is no deep pit on the lateral surface of the entocondyle. The femur may be either slender or stout, but is not markedly curved forwards. The popliteal depression is deep, and the summit of the great trochanter rises considerably above the level of the head. The pelvis approximates to that of the Apterygidae, but the pectineal process of the pubis is less developed, and the ischium and pubis may be longer and more slender. The coracoid and scapula are aborted and may be absent. The sternum, which may be either long and narrow, or broad and short, differs from that of the Apterygidae by the absence of the superior notch, the divergent lateral processes, and the reduction of the coracoidal grooves to small facets or their total disappearance. The cervical vertebrae are relatively short, an expanded neural platform as far as the sixth.

In Anomalopteryx and Megalapteryx the number of cervical vertebrae is 21, and there are 2 cervico-dorsal and 4 free dorsal vertebrae, so it is fair to assume that this is the correct number throughout the family.

The feathers had after-shafts.