GEOLOGICAL DISTEIBUTION. 199 



As already mentioned, tte Oolithic formations show a 

 great similarity of tlieir fish-fauna to that of the Lias ; but 

 still more apparent is its approach to the existing fauna. 

 Teeth have been found which cannot even generically be 

 distinguished from Notidanus. The Eays are represented by 

 genera like Spathdbatis, Belemnolatis, Thaumas; t\ie. Holoce- 

 pJiali are more numerous than in the Lias {Ischyodus, Gan- 

 odus). The most common Ganoid genera are Caturus, 

 Pycnodus, PhoUdophorus Lepidotus, Leptolepis, all of which 

 had been more or less fully represented in the Lias, Also 

 Geratodus is continued into it. 



The Gretaceous group offers clear evidence of the further 

 advance towards the existing fauna. Teeth of Sharks of 

 existing genera Garcharias {Corax), Scyllium, Notidanus, and 

 Galeocerdo, are common in some of the marine strata, whUst 

 Hybodonts and Cestracionts are represented by a small num- 

 ber of species only ; of the latter one new genus, Ptychodus, 

 appears and disappears. A very characteristic Ganoid genus, 

 Macropoma, comprises homocercal fishes with rounded ganoid 

 scales sculptured externally and pierced by promiaent mucous 

 tubes. Gaturus becomes extinct. Teeth and scales of Lepi- 

 dotus (with Sphmrodus as sub-genus), clearly a fresh-water 

 fish, are widely distributed in the Wealden, and finally dis- 

 appear in the chalk ; its body was covered with large rhom- 

 boidal ganoid scales. Gyrodus and Aspidorhynchus occur in 

 the beds of Voirons, Goelodus and Amiopsis (allied to Amra), 

 in those of Comen, in Istria. But the Palseichthyes are now 

 in the minority ; undoubted Teleosteans have appeared, for 

 the first time, on the stage of life m numerous genera, many 

 of which are identical with still existing fishes. The majority 

 are Acanthopterygians, but Physostomes and Plectognaths 

 are likewise well represented, most of them being marine. 

 Of Acanthopterygian families the first to appear are thePery- 



