[Illustration: Fig. 148.--Caturus furcatus (Solenhofen).] SECOND FAMILY--LEPTOLEPIDÆ. _Scales cycloid. Vertebræ ossified; homocercal; fins without fulcra; dorsal short. Teeth minute, in bands, with canines in front._ Extinct, and leading to the living representative of this suborder. _Thrissops_ with the dorsal fin placed far backwards, and opposite to the long anal. _Leptolepis_ with the dorsal fin opposite to the ventrals, from the Lias and Oolite. These fishes, as far as the preserved parts are concerned, cannot be distinguished from Teleosteous fishes, to which they are referred by some Palæontologists. [Illustration: Fig. 149.--Leptolepis sprattiformis.] THIRD FAMILY--AMIIDÆ. _Skeleton entirely ossified; a single large gular plate; homocercal; fins without fulcra; a long soft dorsal fin. Abdominal and caudal parts of the vertebral column subequal in extent. Branchiostegals numerous._ [Illustration: Fig. 150.--Amia calva; _g_, gular plate.] AMIA.--Body rather elongate, sub-cylindrical, compressed behind. Snout short, cleft of the mouth of moderate width. Jaws with an outer series of closely-set pointed teeth, and with a band of rasp-like teeth; similar teeth on the vomer, palatine, and pterygoid bones. Anal short; caudal fin rounded. Gills four; air-bladder bifurcate in front, cellular, communicating with the pharynx. The “Bow-fin” or “Mud-fish” (_A. calva_) is not uncommon in many of the fresh waters of the United States; it grows to a length of two feet. Little is known about its habits; small fish, crustaceans, and aquatic insects, have been found in its stomach. Wilder has observed its respiratory actions; it rises to the surface, and, without emitting any air-bubble whatever, opens the jaws widely, and apparently gulps in a large quantity of air; these acts of respiration are more frequently performed when the water is foul or has not been changed; and there is no doubt that an exchange of oxygen and carbonic acid is effected, as in the lungs of aërial vertebrates. The flesh of this fish is not esteemed. Fossil remains occur in tertiary deposits of North America, for instance in the Wyoming territory; they have been distinguished as _Protamia_ and _Hypamia_. SECOND SUB-CLASS--TELEOSTEI. _Heart with a non-contractile bulbus arteriosus; intestine without spiral valve; optic nerves decussating; skeleton ossified, with completely formed vertebræ; vertebral column diphycercal or homocercal; branchiæ free._[40]