WHITE-FISH, WHITING, WOLF-FISH, WRASSE.
Order 4, Uaneidei.—This is an important order, but is represented more by extinct than by living forms, reaching far back in geological time, and furnishing many of the most interesting studies in paleontology. At the present epoch the order consists of only seven genera, viz.: 1, lepidosteus; 2, polypterus; 3, calamoichthys; 4, amia; 5, ad penser; 6, seaphiMynehus; 7, spatularia; all confined to the northern hemisphere, and principally to fresh water. They have the following characteristics: The endo-skeleton is only partially ossified, most of the vertebral column remaining cartilaginous during life, especially in the paleozoic forms, in which the notochord is often permanent. The skull has distinct cranial bones, and there is a lower jaw-bone. The exoskeleton is in the form of ganoid scales (see GANOID FISHES, ante) or spines. There are usually two pairs of lateral fins, supported by fin rays. the first rays being generally in the form of strong spines. The pectoral arch is furnished with a clavicle, and the ventral fins are close to the anus. The caudal fin is generally unsymmetrical (heterocercal). There is always an air-bladder, which is provided with an air-duct, and is often cellular. The intestine is furnished with a spiral valve. The gills and opercular apparatus resemble those of the teleostei. The heart has one auricle and one ventricle, and the base of the bronchial artery is dilated into a bullies arteriosus, which is rhythmically contractile, and has a coat of striated muscular fibers and several transverse rows of valves. The most important of these characteristics are, the partially ossified condition of the endo-skeleton. but which varies WI to extent of ossification. In most of the older forms the notochord remains, no vertecsal contra are developed, and the skull is cartilaginous and protected by ganoid plates; but even in these the outer parts of the vertebrie are often ossmed. In others the vertebrze are biconcave or amphiccelous, as in teleostei. In one ganoid,
however, the bony pike or lepidosteus, the vertebrae are opisthoccelons, or concave behind and convex in front. This is regarded as the highest point of development in the vertebral column of any fish, and as being more reptilian than piscine. The ganoid scales are composed of two layers, an inferior one of bone, and an outer one of enamel, similar to that of teeth, and called ganoine. The most typical form of these plates is rhomboidal, and placed edge to edge without overlapping, articulated by means of dis tinct processes, and forming oblique rows. Sometimes, however, the plates or scales are circular, and overlap each other as in ordinary fishes. In the sturgeon there are detached dermal plates of true bone. Both pectoral and ventral fins are usually pres ent, the ventrnls being placed far back. In sonic forms the paired fins are arranged so as to form a fringe around a central lobe, and for this reason prof. Huxley has arranged them in a distinct section called erossopterygUlte (fringe-finned). The same form is found in the sixth order, (tiptoe. The caudalfin varies in being sometimes homocercal, and sometimes heterocercal, and therefore, in this respect, the ganoids are midway between the bony fishes (teleostei) and the sharks and rays. Like the bony fishes, the ganoids have free, pectinated gills attached to branchial arches and inclosed in a branchial cham ber protected by gill-cover, and closed by a brauchiostegal membrane, usually sup ported by brancluostegal rays. The sturgeon (aeipenser) and po/ypterild are furnished with spiracles on the top of the head, communicating with the mouth. The order gun siclei may be divided into two sections, lepidoganoidet, in which the body is furnished with scales of moderate size, and the endoskeleton is more or less perfectly ossified ; and plaeoganoidel, in which the skeleton is imperfectly ossified, and the head and more or less of the body are protected by large ganoid plates, often united by sutures. See BONY