Distribution of Primitive Fishes 493 



Carboniferous to late Permian time, till Illinois on the west 

 and Saxony on the east were invaded. 



To return however to the primitive palaeoniscids, these 

 had become extremely abundant series, over a wide con- 

 tinental area, that was evidently fairly continuous from 

 East Canada, Illinois and Ohio, through Britain, France, 

 Belgium and Germany to W. Russia. For the known oc- 

 currence of species of Rhadinichthys, of Amblypterus, and 

 of Gonatodus amongst others from these centres, and that 

 ranged from Calciferous to Upper Carboniferous time, is 

 a fragmentary indication of what once must have been both 

 the abundance and variety of the fish-life, as it is of wide 

 continental territory that these were scattered over. 



The most ancient known genus, Cheirolepis, is, as al- 

 ready noted (p.317) frequent in Lower Old Red beds of 

 North Scotland as C. trailiii, while C. canadensis from 

 Upper Devonian beds of East Canada, proclaims probable 

 descent from a species of W. European origin. 



The Crossopterygii is the only remaining order of the 

 Teleostomi from which evidence for former geographic and 

 geologic connections can be secured. It is also the order 

 that is at once the most primitive and the most persistent 

 through geologic time. For from the first abundant ap- 

 pearance of several genera in the Old Red Sandstone of 

 Scotland, derivative representatives have persisted up till 

 now. The two existing genera Polypterus and Calamich- 

 thys are Central African and freshwater in habitat. For 

 though the one species of Calamichthys is now known to 

 occur along the Cameroon coastal region, this habitat Is 

 clearly derivative and untypical. It Is deserving of passing 

 note here also that the continental distribution of the living 

 dipnoan genus Protopterus is almost Identical with that of 

 the living Polypterus, while the ancestral Dipnoi and Cross- 

 opterygii can equally be traced back to Old Red Rocks. 



But we have already seen that exactly the same distri- 

 butional area of Africa is occupied by several groups of 

 teleostean fishes that are either peculiar to It, or that show 

 close affinity with nearly related South American groups. 

 As yet no living or fossil types of Crossopterygii however 

 are known from the latter continent. In relation to their 



