346 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



group that have succeeded in crossing to the east of Wallace's Line ^ 

 in the East Indies, and in reaching Madagascar.' 



After this second group comes a succession of families of catadromous 

 or anadromous fishes such as the fresh-water eels, the salmon and trout, 

 the sturgeons, the galaxiids and the aplochitonids, and others which, 

 for one reason or another, enter the sea freely and are in most cases not 

 of use in studies of the distribution of fresh-water fishes. Lastly we 

 find primarily marine families such as the sharks, herrings, gray 

 mullets, sea basses, and gobies, a few of whose members have invaded 

 the rivers and sometimes developed into purely fresh-water species. 



THE FRESH-WATER FISH FAUNAS OF THE AMERICAS 



1. LIMITATION TO TERTIARY 



In the mammals, the history of many of the modern orders has 

 been traced back to their very different Eocene ancestors and consider- 

 able has been done in connecting these up with Mesozoic forms. The 

 story of the continental fishes is very different. The Ostariophysi, as 

 well as nearly all other groups of fresh-water bony fishes, are known 

 only as far back as the early Tertiary, and the few known Eocene 

 fossils usually turn out to belong to still living genera or their very 

 close relatives. It would seem that the evolution, from very primitive 

 types into practically modern forms, of a whole series of the major 

 groups of fresh-water (and marine) bony fishes occurred between the 

 end of the Cretaceous and the earlier Eocene. What little we know of 

 Paleocene fishes is mostly from marine deposits, and the derivation 

 and evolutionary lines of the Ostariophysi and most other fresh-water 

 groups remains a closed book. The locating of early Eocene and 

 Paleocene fresh-water beds and the working out of the history of the 

 fishes remains one of the greatest untouched problems in vertebrate 

 paleontology, and one in which American paleontologists, at least, 

 have taken strangely small interest. It is evident that we can draw 

 no definite conclusions regarding pre-Tertiary geography from the 

 fresh-water bony fishes, and but little about post-Mesozoic from such 

 primitive relicts as the lungfishes and bichirs. 



2. NORTH AMERICA 



The greater part of the Tertiary and recent fresh-water fish fauna of 

 North America is divisible into two sections. The first forms the old, 

 endemic fauna composed of paddlefishes, garpikes, bowfins, osteo- 

 glossids, suckers, ameiurid catfishes, primitive cyprinodonts, and 



• It seems probable that the presence of the air-breathing climbing perch (Anabas) east of Wallace's Line 

 is due to human introduction. Anabas is much carried about as a food fish. As to the osteoglossids, see 

 further on. 



' ElToplui, the only Indian cichlid, is confined to the southern Indian Peninsula and is closely related 

 only to certain Madagascan species; it perhaps arrived in India by sea via the Scychelles-Chagos-Maldive 

 chain. 



