Distribution of Primitive Fishes 491 



Wales territory, If not more extensively. So from Massa- 

 chusetts to Virginia on the West, and thence through central 

 Europe to India and N. S. Wales on the east, as well as 

 down to S. Africa, a wonderful similarity of fish-genera can 

 be traced from the upper Triassic till the Llassic or even 

 later. The genera and, It may be, families of these fishes, 

 as we have seen, are constantly changing, as successive 

 geologic strata are passed through, but In any single system 

 of rocks, the very wide extension of the freshwater fish 

 fauna. In genera and at times even In species. Is an arrest- 

 ing fact of fundamental Importance. 



The cartilaginous Actlnopterygll carry us back Into still 

 older geologic strata, and into still older continental land 

 masses. Of the two families Palaeoniscidae and Platysom- 

 idae that compose the group, the former seems to be the 

 older and more primitive, alike as to shape of body, ex- 

 panse of mouth, sectorial teeth, simpler scales and other 

 structural details. But both groups indicate that they 

 gradually came to occupy the same continental habitats 

 from the Lower Carboniferous — or Calclferous — period 

 onward, while all remained freshwater fishes, or only rarely 

 seem to have been anadromous to a slight extent. 



The most extensive and continuous distribution of the 

 two families, according to our present knowledge of fossil 

 remains, occurred from Upper Carboniferous to Triassic 

 time, and the remarkable similarity In this distribution to 

 what has been outlined above for the Semlonotldae, will 

 be at once apparent. Thus Palaeonisciis appears first in 

 the Upper Coal Measures of France; is doubtfully known 

 from the Lower Permian of Hohenelbe, and has been re- 

 ported in different species from the Upper Permian of 

 Durham and Northumberland, of Hannover, of Thurlngia 

 and Saxony, of Kargala In Russia, and from the Karoo beds 

 of Triassic age in S. Africa. 



The related genera Acrolepis, Apateolepis, Gyrolepis, 

 Atherstonia and Alyriolepis, start with the first of these 

 In Scottish Calclferous rocks, while expansion to England, 

 Belgium and Nova Scotia then followed. In the Permian 

 Acrolepis Is reported from East England^ Germany, and 

 Russia, while one species Is reported from the Karoo beds, 



