7 6 EVOLUTION IN THE PAST 



but these did not exhibit in other respects notable 

 advance over their Permian predecessors (Belonorhynchus, 

 Saurichthys). 



The most interesting ganoids were some highly developed 

 forms, a few forerunners of which had appeared in the 

 preceding Period (Acentrophoms'). These possessed vertebral 

 columns well ossified, dorsal and anal fins adequately sup- 

 ported, and tails that were assuming modern character. 

 In short, they possessed all the features of progress evi- 

 dent in fish life ; whilst no other fishes possessed them in 

 entirety. 



Fishes of this type so rare in the Permian were now 

 varied and numerous (Semionotm, Lepidotus). They were 

 for the most part of strange aspect, and not closely com- 

 parable with living fishes. Some very small forms bore a 

 resemblance to herrings (Pholidophorus). Other forms 

 (Caturus) in some respects strongly resembled the bow- 

 fins of our own time (Amia). 



At the close of the Period these various members of well- 

 advanced fish-life became fairly abundant ; but their less 

 highly developed relations suggestive of bottles too old to 

 hold much of the new wine continued predominant. 



Curious old forms, intermediate in development between 

 sharks and lung-fishes (famous in Carboniferous and not 

 insignificant in Permian seas), had now become practically 

 DIPNOANS extinct (Pleur acanthus'). Among dipnoans a few forms had 

 now reached a point at which they differed very little from 

 the Australian " mud-fish " of to-day (Ceratodus). In 

 Triassic times " double-breathers " were abandoning salt 

 water for brackish and fresh. And in this Period they practi- 

 cally made their last appearance as marine fishes. 



AMPHIBIANS The lizard-like Stegocephs were now represented by a 

 variety of forms (Capitosaurus, Trematosaurus'). Large-eyed 

 monsters, too, were among them, with skulls of more than a 

 yard in length (Mastodonsaurus}. Those with teeth of 

 elaborate structure, and named Labyrinthodonts, had greatly 

 increased. Indeed practically all Triassic stegocephs, it 

 would seem, belonged to that group. They were more highly 

 developed than their Permian predecessors, as their back- 



