74 
Gallery, 
No. 6. 
Wall-case, 
No. 5. 
Table-case, 
No. 36. 
Wall-case, 
No. 4. 
Table-case, 
No. 35. 
Wall-cases, 
Nos. 5 to 7. 
Wall-case, 
No. 8. 
Table-cases, 
No. 37-39. 
Wall-cases, 
Nos. 9 to 14 
Pisces — Dipnoi and Ganoidei. 
Order III.— DIPNOI. 
The Dipnoi form a very peculiar order of fishes, having a 
a notochordal skeleton. To it belong the living Protopterus , 
Lepidosiren , and Ceratodus. Teeth, indistinguishable in cha- 
racter from the modern Ceratodus , are abundant in the Trias, 
Rhaetic, and Oolitic formations. Dipterus occurs in the Devonian, 
Ctenodus in the Carboniferous. Several other genera are also 
represented. 
Order IV.— GANOIDEI. 
In Wall-case No. 4 follow the Acantliodians, represented by 
Cheir acanthus, from the Lower Old Red Sandstone of Lethen liar 
and Tynet Burn, and from the equivalent beds of Forfarshire. 
To these succeed the Placoderms (Pterichthys, Coccosteus , 
Asterolepis) , and in Table-cases Nos. 34, 35, are placed many of 
the smaller Acanthodians, and the Cephalaspidce ( Cephalaspis , 
Scaphaspis , Pteraspis, &c.), from the Scottish Old Red, and from 
Herefordshire. Two fine reproductions of the shield of the 
Placoderm Homosteus are also placed on the pillar between 
Wall-cases Nos. 4 and 5. The original specimens were obtained 
from the Lower Old Red Sandstone of Caithness, and are now 
in the Edinburgh Museum. 
In Wall-cases 5 — 15 are arranged the true fishes of the 
order Ganoidei. The first sub-order (Crossopterygii) occupies 
cases 5 to 7, and embraces the Hotoptychiidce ( Ho lopty chius, 
Glyptolepis ) ; Bhizodontidce (Tristichopterus and Gyroptychius 
from the Old Red Sandstone, and Bhizodus from the Lower 
Carboniferous of Scotland) ; the Saurodipteridce (Osteolepis and 
Diplopterus , from the Old Red Sandstone, and Megalichthys from 
the Carboniferous) ; and lastly, the Codacanthidce , remarkable for 
their long range in geological time ( Coelacanthus occurring in 
the Carboniferous and Permian, Holophagus in the Lias, JJndina 
in the Oolites, and Macropoina in the Chalk). 
Wall-case 8, and a portion of No. 7, contain remains of the 
second sub-order of Ganoids, the Acipenseroidei. These are 
represented by the true Sturgeons (Acipenser) from the London 
Clay of Sheppey; by Ghondrosteus and Gyrosteus from the Lias, by 
the Palceoniscidce , including Chirolepis, Pygopterus , Acrolepis, and 
Oxygnathus, from the Old Red Sandstone to the Lias inclusive, 
followed by the Platysomidce, represented by the genus Platysomus. 
Wall-cases Nos. 9 to 14 comprise all the genera included in 
the great sub-order of the Lepidosteoidei (fishes Avith rhom- 
boidal scales) represented by the genera Eugnathus , Lepidotus , 
Heterolepidotus, Dapedius, Pholidophorus , Semionotus , Aspido- 
rhynchus , Gyrodus, &c. 
In Wall-case No. 15 are placed the fossil fishes of the sub- 
Wall-case, 
No. 15. 
