The Ganoids 29 



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 ArchaomcBnidcz differ 

 from Pholidophoridae in having cycloid scales. In both families 

 the vertebrae are reduced to rings about the notochord. From 

 fishes allied to the Pholidophorida the earliest Isospondyli are 

 probably descended. 



In the Aspidorhynchida the snout is more or less produced, 

 the mandible has a distinct presymphysial bone, the vertebrae 

 are double-concave or ring-like, and the fins are without fulcra. 

 This family constitutes the suborder A^theospondyli. In form 

 these fishes resemble Albula and other modern types, but have 



FIG. 22. Pholidophorus crenulatus Egerton. Lias. (After Woodward.) 



mailed heads and an ancient type of scales. Two genera are 

 well known, Aspidorhynchus and Belonostomus. Aspidorhyn- 

 chns- 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. Belono- 

 stomus sphyrccnoides is the best known of the numerous species, 

 all of the Triassic, Jurassic, and Cretaceous. 



Family Lepisosteidae. The family of Lepisosteida, constituting 

 the suborder Ginglymodi (yiyyXv^o?, hinge), is characterized 

 especially by the form of the vertebrae. 



These are opisthocoelian, convex in front and concave behind, 

 as in reptiles, being connected by ball-and-socket joints. The tail 

 is moderately heterocercal, less so than in the Halecomorphi, and 

 the body is covered with very hard, diamond-shaped, enameled 



