Dipnoi
an order of fishes, small in number, but of great importance as exhibiting a distinct transition between the fishes and amphibia. So many are the points of resemblance between the two, that until recently the Lepidosiren was always made made to constitute the lowest class of amphibia. The highest authorities, however, now concur in placing it among the fishes. The order Dipnoi is thus defined: the body is fish-like in shape; there is a skull with distinct DIPPEL cranial bones and a lower jaw, but the notochord is persistent, and there are no vertebral centra, nor an occipital condyle.
The exo-skeleton consists of horny, overlapping scales, having the cycloid character. The pectoral and ventral limbs are both present, but have (in Lepidosiren) the form of awl-shaped, filiform, many-jointed organs of which the former only have a membranous fringe inferiorly. Until recently the only two members of the order were the Lepidosiren paradoxa of South America, and the L. annectens of Africa.