Distribution of Primitive Fishes 485 



age in Wyoming. Probably therefore it existed over at 

 least the central N. American area back into Cretaceous. 

 So in early Eocene time it could spread across the N. At- 

 lantis bridge along with many teleosts already referred to. 

 Remains of several species, however, have been recorded 

 from lower and mid Eocene beds up possibly to Lower 

 Miocene strata of east central Europe. But there the group 

 has since been wholly obliterated. 



Lepidosteus, however, in general morphology, and not 

 least in the highly complex bony constituents of the head 

 and jaws, seems truly to be the end member of a series 

 that included the more ancient Aspidorhynchiis and 

 Belonostomtis. Now, species belonging to one or other 

 of these two can be traced from Upper Cretaceous through 

 Purbeck to Kimmeridgean age, and this over a wide extent 

 of territory. Thus Belonostomtis, while existing apparent- 

 ly for a long period in central S. Europe, has been reported 

 from the Upper Cretaceous of Mexico, from Ceara in 

 Brazil, from Queensland, and in a doubtful specimen from 

 India. 



This lends support to the view that the genus may have 

 branched off from common ancient ancestors with Aspidor- 

 hynchiis, that were native in Western Europe back to the 

 time of deposit of the Stonesfield slates at least. For from 

 these slates J. crassus has been described. So early passage 

 westward across the N. Atlantis bridge, as well as extension 

 eastward into Australia, between Kimmeridgean and Pur- 

 beck time could satisfactorily account for distribution of the 

 Aetheospondylii as a whole. Species representing all three 

 genera then, may have existed side-by-side from central 

 Europe across N. Atlantis to central N. America, as well as 

 eastward through S. Siberia and China to Australia. Pro- 

 gressive modification and southward extension of descend- 

 ants that reached the Southern States may have proceeded, 

 till they invaded the east Brazilian region during the late 

 Cretaceous. A similar journey, however, was being carried 

 out by teleosts of the same or somewhat later period, as 

 has been already indicated. The above three genera then 

 anew emphasize the view that during Jurassic and possibly 

 early Cretaceous age, some extensive systems of freshwater 



