192 NEW YORK STATE MUSEUM 



is therefore held to indicate that there was at least intermittent connection 

 between the two basins during Onondaga time, and persisting well into the 

 Hamilton. It is admitted, however, that the question as to how the stream 

 of migration entered the Hudson Bay area during the Middle Devonic is 

 not so easy to answer.' Precisely at this point some light is thrown on 

 the problem by vertebrate paleontology. A number of specimens of 

 M a c r o p e t a 1 i c h t h y s s u 1 1 i v a n t i ( = M . r a p h e i d o 1 a b i s) are 

 recorded by Bell and Whiteaves from the country immediately west and 

 south of Hudson and James bays.'' This exclusively Onondaga species 

 (Mr Schuchert inadvertently calls it a Hamilton fossil) is most abundant in 

 Ohio and Indiana, and decidedly less common in New York State. The 

 same genus, represented by some two or three species, occurs also in the 

 Eifelian Devonic, which is equivalent practically to the Onondaga, and in the 

 slightly earlier horizon in Bohemia designated as etage G'. No trace of it 

 occurs, however, in the Mesodevonic of the maritime provinces of eastern 

 North America. One may readily infer that this genus and its various associ- 

 ates are indigene in Bohemia, a part of the vertebrate fauna from etage G' 

 being inceptive in etage F'. Thence it spread northeastward into Russia, 

 westward into the Eifel District, and northwestward into the Hudson and 

 James Bay region. From this latter region we may suppose it to have 

 passed southward through Ontario by means of a passageway connecting 

 with the Appalachian gulf over the area that is now occupied by Ohio and 

 Indiana, where the fauna reached its climacteric. The most conspicuous ele- 

 ments of the fauna are Arthrodires and Ptyctodonts, groups which began 

 immediately upon their introduction to attain a most remarkable develop- 

 ment. Throughout the Hamilton and later Devonic, conditions must have 

 been eminently favorable in the Appalachian sea for the further specializa- 

 tion of armor-clad Dipnoans of the type represented by Dinichthys and its 

 congeners. Like their earliest predecessors, they became of greatest 

 importance locally in Ohio. 



'^ Loc. cit. p. 156. 



^Cleol. Sur. Can. Reji't of Progress. 1875-76. p. 319. 



