_Scales ganoid, lozenge-shaped. Skeleton completely ossified; vertebræ convex in front and concave behind. Fins with fulcra; dorsal and anal composed of articulated rays only, placed far backwards, close to the caudal. Abdominal part of the vertebral column much longer than caudal. Branchiostegals not numerous, without enamelled surface. Heterocercal._ _Lepidosteus._--Body elongate, sub-cylindrical; snout elongate, spatulate, or beak-shaped; cleft of the mouth wide; both jaws and palate armed with bands of rasp-like teeth and series of larger conical teeth. Four gills; no spiracles; three branchiostegals. Air-bladder cellular, communicating with the pharynx. [Illustration: Fig. 145.--Lepidosteus viridis.] Fishes of this genus existed already in Tertiary times; their remains have been found in Europe as well as North America. In our period they are limited to the temperate parts of North America, Central America, and Cuba. Three species can be distinguished which attain to a length of about six feet. They feed on other fishes, and their general resemblance to a pike has given to them the vernacular names of “Gar-Pike,” or “Bony Pike.” SECOND FAMILY--SAURIDÆ. _Body oblong, with ganoid scales; vertebræ not completely ossified; termination of the vertebral column homocercal; fins generally with fulcra. Maxillary composed of a single piece; jaws with a single series of conical pointed teeth. Branchiostegals numerous, enamelled, the anterior broad gular plates._ Extinct. Numerous genera occur in Mesozoic formations; one with the widest range is _Semionotus_, with distichous fulcra, from the Lias and Jura; _Eugnathus_, with large posteriorly serrated scales, and fulcra on nearly all fins; _Cephenoplosus_ from the Upper Lias; _Macrosemius_ from the Oolite; _Propterus_, _Ophiopsis_, _Pholidophorus_, _Pleuropholis_, _Pachycormus_, _Oxygnathus_, _Ptycholepis_, _Conodus_, _Eulepidotus_, _Lophiostomus_, etc. THIRD FAMILY--STYLODONTIDÆ. _Body rhombic or ovate, with ganoid scales; vertebræ not completely ossified; termination of the vertebral column homocercal; fins with fulcra. Maxillary composed of a single piece; jaws with several series of teeth, the outer ones equal, styliform. Dorsal fin very long, extending to the caudal. Branchiostegals numerous._ Extinct. _Tetragonolepis_ from the Lias (see Fig. 103, p. 207). FOURTH FAMILY--SPHÆRODONTIDÆ. _Body oblong, with rhombic ganoid scales; vertebræ ossified, but not completely closed; homocercal; fins with fulcra. Maxillary composed of a single piece; teeth in several series, obtuse; those on the palate globular. Dorsal and anal fins short. Branchiostegals._