FRESHWATER FISH FAUNA 219 



United States, are clearly of northern origin, hut whether Eurasian 

 or American is problematical. Hence they are not included in the 

 above estimates. Darters (Etheostomatinae) are considered North 

 American, but the three other large percids are tentatively assigned 

 a Eurasian origin. 



In western North America there are an equal number of families 

 of North American and Eurasian origin but the three Eurasian 

 groups (Umbridae, Cyprinidae, and Catostomidae) account for 97 

 per cent of the primary fauna. The rather sharp differences between 

 the western and eastern American fish faunas are of relatively re- 

 cent origin, probably post-Miocene except for the three old lowland 

 relicts, Novumbra, Columbia, and Archoplites. Excluding the very 

 recent. Postglacial eastern invaders, there is an overlap of only about 

 5 per cent in the total number of species between the two regions. 



Acknowledgments 



During the approximately 20-year period that I have been studying 

 western fishes, Dr. Cad L. Hubbs has provided guidance and repeated 

 stimulation both by encouragement of my work and through our joint 

 studies. He has also criticized this manuscript. Although I accept full 

 responsibility for the conclusions here expressed, my indebtedness to him 

 is considerable. My colleague. Dr. Reeve M. Bailey, has also made valued 

 suggestions for improving the manuscript and has generously allowed me 

 to use the map (Fig. 1) which he compiled and which appears here with 

 only minor modifications. Dr. Leonard P. Schultz kindly arranged for the 

 use of photographic copies of certain original drawings (Figs. 4, 7, 13, 

 18-19). Research grants from the Horace H. Rackham School of Graduate 

 Studies, University of Michigan, made possible much of the field work 

 that provided the raw data for this report. The maps and charts were 

 drafted by Mrs. Betty Anthony. 



REFERENCES 



Bailey, Reeve M. 1956. A revised list of the fishes of Iowa, with keys for 



identification, in James R. Harlan and Everett B. Speaker, Iowa 



Fish and Fishing. Iowa State Conserv. Comm., 3rd edition, pp. 327- 



377. 

 Berg, Leo S. 1936. The suborder Esocoidei (Pisces). Bull. inst. recherches 



biol. Perm, 10: 385-391 (in Russian and English). 

 — -. 1949. The freshwater fishes of the USSR and neighboring regions. 



Acad. Nauk Moscow, 2: 469-924, Figs. 288-674 (in Russian). 

 Blackwelder, Eliot. 1948. The geological background, in The Great Basin, 



with emphasis on Glacial and Postglacial times. Bull. Univ. Utah, 38 



(20): 3-16. 



