LEPIDOSIREN is the name of one of the most remarkable genera of fishes, of which one species (Lepidosiren paradoxa) has been found in tributaries of the river Amazon, and the other (Lepidosiren annectens) occurs in the systems of all the large rivers of tropical Africa. The latter species differs in some points, notably in having six instead of five branchial arches, from L. paradoxa, and therefore has been generically separated by Owen under the name of Prοtopterus,— which name likewise is in common use. Together with the Australian Ceratodus, the lepidosirens are the only living representatives of a very old type of fishes, the Dipnoi, which reaches back to the Devonian age, thus giving us an insight into the organization of fishes of which nothing but some obscure and fragmentary impressions of the hard parts are preserved. The body of Lepidosiren is eel-shaped, and covered with small thin scales. A single vertical fin surrounds the posterior part of the body and the tail; the paired fins are reduced to two pairs of long threads, internally supported by a series of small cartilages. The dentition is very characteristic, and consists of a pair of conical pointed vomerine teeth, and a pair of large cuspidate and ribbed molar teeth on the palate and in the lower jaw. The skeleton is notochordal; and lungs are present in addition to gills. From this latter fact it may be inferred that the lepidosirens can breathe air as well as water; and, although they have never been observed to leave the water voluntarily, either in a state of nature or in captivity, they rise from time to time to the surface to fill their lungs with a fresh supply of air; further, when, during the hot season, the water of the tanks in which they live changes into mud, branchial respiration is ...