UPPER PERMIAN, TRIASS1C, AND RHMTIC. 415 



of a very uniform character, and distributed over a large part 

 of Europe and North America, while there are slight traces 

 of it also in Central Asia. The limestones deposited in the 

 deeper waters yield remains of Elasmobranch fishes with a 

 powerful crushing dentition (Psaminodus and the Cochliodon- 

 tidse). Other sharks are also abundant, especially the Ichthyo- 

 tomi (Pleur acanthus) \ and a few highly specialized Acanthodians 

 still remain, though these become extinct with the genus 

 Acanthodes in the Permian. The Arthrodira have now dis- 

 appeared, but the Dipnoi are as numerous as before (Ctenodus). 

 Of the Crossopterygian fishes the Holoptychiidae are wanting, 

 but the Rhizodontidae and Osteolepidae are abundant, and the 

 remarkable Ccelacanthidae first appear (Coelacanthus). The 

 Palaeoniscidae and Platysomidse, however, are the dominant 

 fishes of the period and mark the dawn of the supremacy of 

 the order Actinopterygii. 



UPPER PERMIAN, TRIASSIC, AND RH^TIC. 



One fish in the Upper Permian of Europe (Acentrophorus) 

 indicates the beginning of the Actinopterygian sub-order of 

 Protospondyli, which becomes dominant in the Jurassic and 

 continues to be of importance until the upper part of the 

 Cretaceous. The Triassic and Rhaetic Teleostomi are perhaps 

 about equally divided between the Chondrostei and the Proto- 

 spondyli, apparently mingled with a few forerunners of- the 

 still higher order of Isospondyli ; and this mingling is observed 

 not only in Europe and North America, but also in New South 

 Wales. The most noteworthy feature of the fauna, however, is 

 the last important appearance of the Dipnoi (Ceratodus) among 

 marine fishes. Ceratodont teeth occur abundantly in Triassic 

 or Rhaetic strata in England and Germany and in India, less 

 abundantly in South Africa and New South Wales; but the 

 only known specimens from later marine strata are two dimi- 

 nutive teeth from the Lower Jurassic of England and a few 

 from corresponding strata in Colorado, U.S.A. 



While the Upper Permian and Triassic fish-faunas were 

 flourishing, undoubted reptiles began to multiply on the land, 



