The Chondrostei and Holostei 343 



the same slab, specimens of the two divisions may be got. 

 This condition holds also, throughout the entire geologic 

 record, up to the close of the Jurassic, when the above seven 

 genera disappear as such. It follows therefore that both 

 groups were freshwater in habitat, and this is fully con- 

 firmed when detailed study of the known species as well 

 as genera, is made. 



From the Ladinian or Lower Mid Trias of Perledo in 

 Lombardy, and even more abundantly from the somewhat 

 higher beds of Raibl in Carinthia, also from Besano in 

 Lombardy, at least five species of Pholidophorus have been 

 secured. These are found side by side with species of the 

 Eugnathidae, Macrosemiidae, Semionotidae, and Belonor- 

 hynchidae. The beds — hitherto treated as marine — are as 

 already indicated (p. 329) typically freshwater, and so we 

 accept it that the earliest isospondylian fishes originated 

 amid freshwaters, and probably as offshooitis from the 

 Semionotidae. 



But Pholidophorus again is associated In the Raibl, the 

 Besano, and the Perledo beds with PhoUdopleurus and 

 usually also with Peltopleurus, while Thoracopterus In the 

 Raibl beds Is alongside species of PhoUdopleurus and Pelto- 

 pleurus that are also common to the Besano beds. So the 

 conclusion is clearly justified that all four genera were fully 

 established, in lakes of the Keuper period. But while some 

 barrier seems to have prevented their passage westward be- 

 yond Britain to N. America, Pholidophorus ^ Peltopleurus 

 and derivative genera reached Australia, and there persist- 

 ed through Jurassic times, in strata that are acknowledged 

 to be freshwater. From these strata also Woodward has 

 described the as yet purely Australian Archaeomene. 



Persisting also in central Europe through Liassic and 

 Kimmeridgian rocks, the Pholidophorldae seem to have 

 been richest In species and individuals, during deposition 

 of the early Purbeck beds. For In Central-South England 

 Pholidophorus, Pleuropholis and Ceramurus are all found, 

 intermixed with the land or freshwater organisms already 

 described (p. 192). 



But meanwhile the more highly organized and more 

 perfectly ossified families Leptolepidae and Oligopleurldae 



