SUMMARY AND CONCLUSION. 257 



corresponding formations in Westphalia and elsewhere. Most of the Scylliidas 

 and Lamnidae are evidently referable to genera which survive in existing seas, 

 though one of these, Scapanorhynchus, is now rare and restricted in its range. 

 The extinct genus Oorax is especially noteworthy, because its vertebral centra are 

 very similar to those of the existing basking shark, Selache, while the teeth of one 

 of the latest species, Oorax affinis, approach those of Selache in shape and might 

 easily be modified into the latter. Gorax may indeed be the Cretaceous ancestor 

 of the Tertiary Selache. Gestracion seems to have undergone no essential change 

 during its long existence from the Upper Jurassic to the present day ; but the 

 typically Cretaceous Hybodont, Synechodu.s, survived only until the Eocene. 

 PtycJwdus is a primitive skate, represented for the most part by gigantic species, 

 which occur only in the Upper Cretaceous, and seem to have become extinct 

 before the end of the period. Though common in the Chalk of England and 

 North iVmerica, its remains have not hitherto been found in the prolific fish-beds 

 of Westphalia, the Lebanon, or Persia. Its Lower Cretaceous predecessors remain 

 unknown, but certain Upper Cretaceous fossils suggest that some descendants may 

 be found among the Tertiary and Recent Myliobatidee. 



As a whole, therefore, the Cretaceous fish-fauna is much more modern in 

 aspect than the contemporaneous reptile-fauna and mammal-fauna; and in its 

 latest phase the Acanthopterygians at least must have undergone remarkably 

 rapid evolution. 



