324 Evolution and Distribution of Fishes 



equals in number the opposed dermal rays. Such being 

 the case, here is an interesting illustration of the common 

 law, that the links between a lower and a higher group 

 are not to be sought among the specialized types of the 

 former, but among those with the most generalized second- 

 ary characters." 



In line with the above then, and looking to the long 

 persistence and wide distribution of Palaeonisciis, it seems 

 likely that the Catopteridae evolved as three slightly diverg- 

 ing genera during the late Permian or early Triassic period, 

 and possibly in central Europe. Following the freshwater 

 streams of travel taken by other groups, as already out- 

 lined, the species of Dictyopyge radiated out gradually into 

 Britain, Ireland, and EaiStern America, also southward 

 by Switzerland and Lombardy — where Perleidiis is met 

 with — into South Africa and New South Wales. It may 

 well be that the nearly allied Catopterus evolved as a side- 

 line from Dictyopyge, as the latter migrated westward to 

 America. For the remote position of the dorsal fin in 

 Catopterus is an advance on Dictyopyge and the palaeo- 

 niscids generally, though some of Newberry's figures — e.g. 

 of C. gracilis — do not well seem to demonstrate the 

 difference. 



The strata in which all of them have been found are 

 fresh-water. Thus Newberry in describing D. macroura 

 from the Triassic coal field of Richmond, Va., says that 

 there it is very abundant; for one slab of shale, formerly 

 belonging to the Lyceum of Natural History, though scarce- 

 ly more than a foot square, carried impressions of over 

 twenty individuals. The Karoo and the N. S. Wales beds 

 are also accepted as freshwater; while Newberry to some 

 extent, and Eastman fully, agreed that those of Eastern 

 America are. 



The next group — the Belonorhynchidae — includes fishes 

 of Lower Triassic to Upper Liassic age. In structure also 

 the only two genera Belonorhynchiis and Saurichthys are 

 highly modified fishes. Woodward says of them: "If these 

 are not degenerate Chondrosteans, they must be abnormally 

 modified Crossopterygians as suggested by O. M. Reis" 

 {i6g: Introd. VIII). The former is one of the character- 



