Intermediate between the allies of the gars and the modern herrings is the large extinct family of _Pholidophoridæ_, referred by Woodward to the _Isospondyli_, and by Eastman to the _Lepidostei_. These are small fishes, fusiform in shape, chiefly of the Triassic and Jurassic. The fins are fringed with fulcra, the scales are ganoid and rhombic, and the vertebræ reduced to rings. The mouth is large, with small teeth, and formed as in the _Isospondyli_. The caudal is scarcely heterocercal. [Illustration: FIG. 19.—_Caturus elongatus_ Agassiz. Jurassic. Family _Isopholidæ_. (After Zittel.) ] [Illustration: FIG. 20.—_Notagogus pentlandi_ Agassiz. Jurassic. Family _Macrosemiidæ_. (After Woodward.) ] [Illustration: FIG. 21.—_Ptycholepis curtus_ Egerton. Lias. Family _Isopholidæ_. (After Woodward.) ] Of _Pholidophorus_, with scales joined by peg-and-socket joints and uniform in size, there are many species. _Pholidophorus latiusculus_ and many others are found in the Triassic of England and the Continent. _Pholidophorus americanus_ occurs in the Jurassic of South Dakota. _Pleuropholis_, with the scales on the lateral line, which runs very low, excessively deepened, is also widely distributed. I have before me a new species from the Cretaceous rocks near Los Angeles. The _Archæomænidæ_ differ from _Pholidophoridæ_ in having cycloid scales. In both families the vertebræ are reduced to rings about the notochord. From fishes allied to the _Pholidophoridæ_ the earliest _Isospondyli_ are probably descended. [Illustration: FIG. 22.—_Pholidophorus crenulatus_ Egerton. Lias. (After Woodward.) ] In the _Aspidorhynchidæ_ the snout is more or less produced, the mandible has a distinct presymphysial bone, the vertebræ are double-concave or ring-like, and the fins are without fulcra. This family constitutes the suborder _Ætheospondyli_. In form these fishes resemble _Albula_ and other modern types, but have mailed heads and an ancient type of scales. Two genera are well known, _Aspidorhynchus_ and _Belonostomus_. _Aspidorhynchus acutirostris_ reaches a length of three feet, and is found in the Triassic lithographic stone of Bavaria. Other species occur in rocks of Germany and England. _Belonostomus_ has the snout scarcely produced. _Belonostomus sphyrænoides_ is the best known of the numerous species, all of the Triassic, Jurassic, and Cretaceous. =Family Lepisosteidæ.=—The family of _Lepisosteidæ_, constituting the suborder _Ginglymodi_ (γιγγλυμός, hinge), is characterized especially by the form of the vertebræ.