CRETACEOUS PERIOD 105 



as in later forms. Other members of the group were de- 

 veloping in the direction of eagle-rays, or " devil " fishes 

 {Ptychodus). 



Dipnoans or fishes of the lung-breathing type had retired dipnoans 

 from the seas to take up permanent quarters in fresh waters ; 

 and no great future was in store for them. 



Among the fringe-finned ganoids (Crossopterygii), one ganoids 

 family — very little changed from Devonian times— con- (cROSSOP- 

 tinued in some force for the greater part of the Period, and terygians) 

 then dwindled to extinction (CcelacanthidcB). Other forms 

 remained ; but fishes of this Order were not destined to 

 lake much part in the finny life of the future ; and it will 

 not be necessary to refer to them in subsequent Periods. 

 Their decline continued in after times ; but they have 

 struggled on, and are represented to-day by one small 

 family, whose members are found in a few rivers of Africa 

 (PolypteridcB). 



The flexibly finned ganoids (Actinopterygii) had been (actinop- 

 exhibiting advances in development ever since Devonian terygians) 

 limes, and had become well established in a variety of forms 

 in the Jurassic. Towards the close of that Period a small 

 number of them had attained the condition of being true 

 bony fishes ; and were, indeed, the immediate heralds of a 

 great revolution. 



During early Cretaceous times steady progress was no 

 ■doubt made ; but there is not much direct evidence as to 

 this. It is clear, however, that when the Period was well 

 advanced, bony fishes gained a decided predominance over 

 the ganoids that had not attained the higher anatomical 

 standard. Ganoids thus became reduced to the long-decadent 

 fringe-finned forms, the flexibly finned fishes more or less 

 resembling sturgeons, and bow-fins, and a few other t5rpes 

 not closely comparable with living fishes. 



Among the bony fishes shoals of herring of various species teleosteans 

 were in evidence (Pseudoheryx, Histiothrissa, etc.). Some 

 large related forms with stout pointed teeth were also in 

 the seas, living probably at the expense of their small rela- 

 tions (Portheus, Saurodon). These formidable fishes attained 

 in some cases a length of six feet ; and somewhat resembled 



