24 



Fossil Fishes. 



Wall -case, 



No. 7. 



their long range in geological time, Ccelaeanthus occurring in the 

 Coal-measures, the Permian and the TJpper Oolite ; Holophagus in the 

 Lias, TJndma in the Oolites (Fig. 54), and Macropoma in the Chalk 

 formation (Fig. 55). The walls of the air-bladder appear to have 

 been ossified in these fishes, as is well seen in several specimens of 

 the series of Macropoma. 



Fig. 54.— Undina Kohleri, Lias (restored outline after Huxley), a, jugular plates; 

 b, the ossified air-bladder ; c, the pelvic bones. 



Fig. 55.— Macropoma, Chalk, Lewes (restored outline after Huxley), a, jugular 

 plates ; b, the ossified air-bladder ; c, the pelvic bones. 



Suborder II. — Acipenseroidei. 



The Acipenseroidei are represented by Acipenser* the Sturgeons, 

 of which there are twenty species frequenting European, Asiatic, 

 and American rivers. The skeleton in these fishes is notochordal ; 

 the skull is cartilaginous, with dermal ossifications and scutes. 



* To this family also belong Scaphirhynchus, Polyodon, and Psephurus, found 

 in the rivers of Asia and North America. 



