The class of Birds comprehends 930 species, which are characterized by the colours of the plumage, the forms of the feathers, the existence of wattles, spurs, and various other circumstances. The third class, _Amphibia_, is composed of animals not, strictly speaking, capable of living both in air and in water, but having the power of suspending their respiration in a more arbitrary manner than others. They are arranged under four orders:-- I. REPTILES. Amphibious animals respiring through the mouth by means of lungs; and furnished with four feet. To this order belong the tortoises, dragons, crocodiles, lizards, toads, and frogs, which are disposed into four genera, containing 83 species. II. SERPENTES, _Serpents_. Respiring through the mouth by means of lungs; destitute of feet, fins, and ears. There are six genera, and 132 species. III. MEANTES, _Gliders_. Respiring by means of gills and lungs; furnished with feet and claws. There is only one species, the lizard-syren of Carolina. IV. NANTES, _Swimming Amphibia_. Respiring at will by means of gills and lungs: the rays of the fins cartilaginous. These animals, of which 76 species are enumerated, are referred to fourteen genera,--the lamprey, ray or skate, shark, chimaera, frog-fish, sturgeon, lump-fish, oldwife-fish, bonyskin-fish, sun-fish, porcupine-fish, trumpet-fish, pipe-fish, and dragon-fish. The number of species described as belonging to this class is 292. The specific characters are derived from various circumstances connected with the external conformation; in the tortoises, from the shell and feet; in the snakes, from the number of the abdominal and caudal plates; in the swimming amphibia, or, as they are now more properly called, the cartilaginous fishes, from the form of the body, the differences of the fins, and other circumstances. The fourth class, that of FISHES, contains four orders, founded upon the relative position of the fins, which are compared to the feet of other animals. Thus, the ventral fins may be placed before, beneath, or behind the pectoral, or they may be wanting. I. APODES, _Apodal_ or _Footless_. Fishes destitute of ventral fins; such as the eel, the wolf-fish, and the sword-fish. II. JUGULARES, _Jugular_. Fishes having the ventral fins placed before the pectoral; as the dragonet, weever, cod, haddock, and coal-fish. III. THORACICI, _Thoracic_. Fishes having the ventral fins placed under the pectoral; as the goby, bull-head, holibut, gilt-head, perch, mackerel, &c. IV. ABDOMINALES, _Abdominal_. Fishes having the ventral fins placed on the abdomen behind the pectoral fins; as in the salmon, trout, pike, mullet, and herring.