Distribution of Primitive Fishes 487 



of travel taken by many fishes reached E. Brazil, only to 

 be later obliterated there as well as in Europe. 



With five such genera now before us as Beloyiostomiis, 

 A spidorhynchiis , Lepidosteus, Megaluriis, and Amia, the 

 question might well be asked whether their distribution was 

 wholly effected by freshwater pathways or whether they 

 were aided and even hastened in distribution by the adop- 

 tion of an anadromous habit, as with the salmon, or wheth- 

 er they were originally marine, and after spreading along 

 coast lines passed gradually into inland waters, in several 

 distinct centres. The last possibility involves so many un- 

 likely and strained relations that we are compelled to re- 

 ject it. The second would be very helpful, if it can be 

 proved to have existed, and in the case of the salmon and 

 sea-trout amongst teleosts, such a capacity has undoubtedly 

 greatly aided in dispersion from primitively freshwater 

 habitats, as already observed (p. 358). But Lepidosteus 

 and Amia are, and evidently both have been, freshwater 

 fishes, alike as to their phylogeny, their habitat, their as- 

 sociated organisms of rock strata, and their present-day 

 tendencies. 



Belonostomus and Aspidoj-Jiynchus were — as already 

 explained (p. 339) — primitively freshwater genera, but 

 became in the Cretaceous period anadromous, or in such 

 species as B. lesinaensis, B. cinctiis and A. euodus, apparent- 

 ly marine. It seems not unlikely then that an anadromous 

 habit may have been developed by some, at least temporari- 

 ly. But no such evidence has as yet been adduced for 

 Lepidosteus and Amia, which extended geographically 

 as freshwater genera, during Eocene to Miocene time, from 

 Wyoming to Central Germany at least. If this be demon- 

 strably true for these genera, it may equally be for their 

 allies. 



Such organic continuity not only suggests more or less 

 continuous land connections, it equally suggests a river, 

 lake, and flood plain continuity for 4000-6000 miles. But 

 were the head-waters or the lower reaches of two such 

 rivers as the Lena, the Yenisei, the Nile, the Amazon, or 

 the Mississippi to be connected even for a time by flood- 

 plain waters, as almost certainly were the Nile and Congo; 



