A Guide to the Study of Fishes, Volume 2 (of 2)

by David Starr Jordan

Fig. 19.—Caturus elongatus Agassiz. Jurassic. Family Isopholidæ. (After Zittel.)

Fig. 20.—Notagogus pentlandi Agassiz. Jurassic. Family Macrosemiidæ. (After Woodward.)

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.

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.