Extinct. The type genus of this family is _Lepidotus_, so named from its large rhombic, dense, and polished scales. The dorsal is opposite to the anal, and all the fins are provided with a double row of fulcra. This genus ranges from the Lias to the Chalk; one species would seem to have survived into tertiary times, if it should not prove to be a _Lepidosteus_. FIFTH FAMILY--ASPIDORHYNCHIDÆ. _Body elongate, with ganoid scales; jaws prolonged into a beak; termination of the vertebral column homocercal. Fins with fulcra; a series of enlarged scales along the side of the body. Dorsal fin opposite to the anal._ [Illustration: Fig. 146.--Aspidorhynchus fisheri, from the Purbeck beds; _m_, mandible; _a_, presymphyseal bone.] Extinct; mesozoic. _Aspidorhynchus_ has the upper jaw longer than the lower; very peculiar is the occurrence of a single, solid, conical bone, situated in front of the symphysis of the lower jaw, to which it is joined by a suture. _Belonostomus_ with both jaws of equal length. SIXTH FAMILY--PALÆONISCIDÆ. _Body fusiform, with rhombic ganoid scales. Notochord persistent, with the vertebral arches ossified. Heterocercal. All the fins with fulcra; dorsal short. Branchiostegals numerous, the foremost pair forming broad gulars. Teeth small, conical, or cylindrical._ Extinct. Many genera are known; from the Old Red Sandstone--_Chirolepis_ and _Acrolepis_; from Carboniferous rocks--_Cosmoptychius_, _Elonichthys_, _Nematoptychius_, _Cycloptychius_, _Microconodus_, _Gonatodus_, _Rhadinichthys_, _Myriolepis_, _Urosthenes_; from the Permian--_Rhabdolepis_, _Palæoniscus_, _Amblypterus_ and _Pygopterus_; from the Lias--_Centrolepis_, _Oxygnathus_, _Cosmolepis_, and _Thrissonotus_. [See Traquair, “The Ganoid Fishes of the British Carboniferous Formations.” Part I. _Palæoniscidæ._] SEVENTH FAMILY--PLATYSOMIDÆ. _Body generally high, compressed, covered with rhombic ganoid scales arranged in dorso-ventral bands. Notochord persistent, with the vertebral arches ossified. Heterocercal; fins with fulcra; dorsal fin long, occupying the posterior half of the back. Branchiostegals numerous. Teeth tubercular or obtuse._ Extinct. From Carboniferous and Permian formations--_Eurynotus_, _Benedenius_, _Mesolepis_, _Eurysomus_, _Wardichthys_, _Chirodus_ (M’Coy), _Platysomus_. [See Traquair, “On the Structure and Affinities of the Platysomidæ”, in “Trans. Roy. Soc.,” Edinb., vol. xxix.] [Illustration: Fig. 147.--Platysomus gibbosus.] EIGHTH SUB-ORDER--AMIOIDEI. _Vertebral column more or less completely ossified, heterocercal. Body covered with cycloid scales. Branchiostegals present._ FIRST FAMILY--CATURIDÆ. _Notochord persistent, with partially ossified vertebræ; homocercal; fins with fulcra. Teeth in a single series, small, pointed._ Extinct. _Caturus_ from the Oolite to the Chalk.