26 



Fossil Fishes. 



Wall-case, 

 No. 7. 



Wall-case, 

 No. 8. 



Table-cases, 



The fossil representatives of the Acipenseroidei are as follows : 



Bony plates of Acipenser (Fig. 56) occur in the London Clay of 

 Sheppey and in the Suffolk Crag. 



The Chondrosteidce, with a single genus, Chondrosteus, in the Lias 

 of Lyme Regis, Dorsetshire (Fig. 62). 



The Palceoniscidce y in which the body is covered with rhombic, 

 ganoid, and often beautifully sculptured scales, the caudal fin being 

 completely heterocercal and Sturgeon-like. 



One genus, Cheirolepis, remarkable for its very minute scales, is 

 known from the Old Red Sandstone. The family attained its 

 Nos. 37 to 39. max j mum i n the Carboniferous formation, being represented by 

 Elonicldhys, Phadinichthys, Nematoptyclvius and Gonatodus. 



To these several new genera have been recently added from the 

 Lower Carboniferous of Eskdale, Dumfriesshire. 



Palceoniscidce are also abundant in the Permian rocks both of 

 England and the Continent (Fig. 61). 



In the Magnesian Limestone of Durham we have Pygopterus, 

 Acrolepis, and Palceoniscus ; these also occur in the Kupferschiefer 

 of Germany, and in the unteres-Rothliegendes Amblypterus (Fig. 57) 

 and Rhabdolepis are found. In Fig. 57 are given views (a) of four 



Fig. 57.— Ganoid scales of Amblypterus striatus, Carboniferous. 



Wall-case, 

 No. 8. 

 Table-case, 

 No. 39, 



of the scales, showing the outer surface, and (b) of two of the 

 scales, showing the inner surface. Each of the rhomboidal ganoid 

 scales of Amblypterus has a ridge on the inner surface which is 

 produced at one end into a projecting peg which fits into a notch 

 in the next scale, reminding one of the manner in which tiles are 

 pegged together on the roof of a house. The Triassic scales known 

 as Gyrolepis, and the teeth named Saurichthys, probably both 

 belong to a Palaeoniscid fish (Traquair). In the English Lias are 

 found Oxygnathus, Cosmohpis, and Thrissonotus. The Palceoniscidce 

 do not extend upwards beyond the Jurassic. 



The Platysomidce are most nearly related to the Palceoniscidce. 

 They are confined to the Carboniferous and Permian formations. 



Platysomus (Fig. 58), Furynotiis (Fig. 59), IFardicMhys, Cheiro- 

 dus (Amphicentrum) (Fig. 60), Mesolepis, Penedenius, Eurysomus, 

 are placed here, and perhaps also Dorypterus. 



