'4 



PISCES 



CLASS T 



Family 2. Acipenseridae. 



Sturgeons. 



Elongated fishes with a produced snout, and small toothless mouth without pre- 

 maxilla. Parietal and frontal bones large, nonsymmetrical, and granulated. Oper- 

 culum incompletely developed, not quite covering the branchial opening ; branchiostegal 

 rays absent. Dorsal and anal fins borne by two roivs of sujjports (axonosts and 

 baseosts) ; ca udal fin strongly heterocercal, the large upper lobe ridged with fulcral 

 scales. Trunk with five longitudinal series of keeled bony plates. Tertiary and 

 Recent. 



The sturgeons of the two living genera, Acipenser and Scaphirhynchus, 

 inhabit the seas of the northern hemisphere, and enter the rivers of Europe, 

 Asia, and North America. Fossil remains are rare. An Eocene species 

 (Acipenser toliapicus, Ag.) is represented by scutes in the London Clay of 

 Sheppey. Scutes and pectoral fin rays are also known from Upper Eocene 

 and later deposits in Europe, and from the Miocene of Virginia, U.S.A. 



Family 3. Polyodontidae. Paddle-fishes. 



Snout very long and spatulate. Parietal and frontal bones paired. Mouth 

 large, with minute teeth in both jaws; no premaxilla. Branchiostegal rays absent. 

 Scales rudimentary or absent, except on the sides of the upper caudal lobe, which is 

 ridged with large fulcral scales. Cretaceous (?) or Eocene to Recent. 



Crossopholis, Cope. Rostrum covered with small stellate bones. Scales of 

 trunk small, thin, and separated ; each being a grooved disc with posterior 

 denticulations like a fringe. C. magnicaudatus, Cope ; Eocene (Green River 

 Shales), Wyoming. 



Pholidwrus, Sm. Woodw. Known by caudal ridge scales only, from the 

 Upper Chalk, Kent. 



Polyodon (Spatularia) living in the Mississippi, Psephurus in Chinese rivers. 



Family 4. Belonorhynchidae. Smith Woodward. 1 



Slender fishes with a much elongated, pointed snout. Mouth very large, and 

 jaws with numerous conical teeth of different sizes. Opercular apparatus reduced, 

 without branchiostegal rays. Fin fulcra minute or absent ; dorsal and anal fins 

 small and remote ; caudal fin diphycercal. Trunk with four longitudinal rows of 

 small, keeled, scale-like plates. Trias and Lias. 



Belonorhynchus, Bronn. (Ichthyorhynchus, Bellotti ; Saurorhynchus, Reis.), 



Fig. 133. 

 FMonorhynehus striolatus, Bronn. Keuper; Raibl, Carinthia. Nat. size. 



(Fig. 133). Head and trunk excessively elongated. Jaws approximately 

 equal in length, and mandible remarkably deep behind. Head bones exter- 



1 Woodward, A. S., The Fossil Fishes of the Hawkesbury Series (Mem. Geol. Surv. N. S. 

 Wales, Palaeont. No. 4), 1890.— Reis, 0., Geogn. Jahresh., IV. Miinchen, 1891. 



