FISHES OF DOUGLAS LAKE, MICHIGAN. 247 



For the purpose of discussing the general distribution of the fishes of Illinois, 

 Forbes and Richardson have divided the region over which they occur into 12 districts 

 and have tabulated the distribution of each species in these districts. The number of 

 Douglas Lake species found within each of these districts is shown in table x, arranged 

 in numerical order. 



Table X. — Showing Number op Douglas Lake Fishes Found in Other Regions. 



Great Lakes basin 22 



Upper Mississippi and Missouri Valleys 21 



Lower Mississippi and Ohio Valleys 20 



Quebec and New England jo 



North Atlantic, New England to Chesapeake Bay ly 



South Atlantic, Chesapeake Bay to Florida j, 



Hudson River 12 



Far north, north of Mississippi drainage, between Rock-y Mountains and Lake Superior drainage. . . 13 



East Gulf district, to Mississippi drainage on west 10 



West Gulf district, westward from Mississippi drainage, including Rio Grande 4 



Florida Peninsula , 



Far northwest, west to Rocky Mountains j 



It is clear from the table that the Douglas Lake species are northern and north- 

 eastern rather than southern or southwestern in their range. A single species, the 

 pike, crosses the Rocky Mountains into the far northwest, but the species is of common 

 occurrence in the Northern Hemisphere. Three species, the large-mouthed bass, the 

 bluegill, and the bullhead, occur in Florida, while four species are found in the west 

 Gulf and Rio Grande region. All the Douglas Lake species, with the exception of the 

 Cisco, occur in the upper Mississippi and Missouri Valleys. In the lower Mississippi and 

 Ohio Valleys all are found, with the exception of the cisco and Etheostoma iowce. In 

 Quebec and New England Etheostoma iowcB, Notropis cayuga, and the bluegill are lack- 

 ing. These three, with the cisco and the miller's thumb, are lacking in the north 

 Atlantic district, leaving 17 species. This number is reduced to 13 in the south Atlantic 

 district, ID in the east Gulf, and 4 in the west Gulf district. 



In general, more Douglas Lake species are to be found in clear, rock and sand- 

 bottomed, northern waters than in the more turbid southern and southwestern waters. 

 Forbes and Richardson (1908) publish a list of 34 Illinois species that avoid the turbid 

 waters of the lower Illinoisan glaciation. Ten of these are also Douglas Lake species. 

 They give also a list of 37 species that tolerate the lower Illinoisan glaciation. In this 

 list are but two Douglas Lake species. 



The fishes of Douglas Lake appear, then, to give preference in Illinois, and pre- 

 sumably elsewhere, to those conditions of water and bottom that are available to them 

 in Douglas Lake and to be distributed over the continent in districts in which such 

 conditions are found. 



SUMMARY. 



1. Four fish habitats are provisionally recognized in Douglas Lake — the barren 

 sand-shoal, the barren stony-shoal, the vegetation, and the deep-water. Each is defined 

 (pp. 221, 222). 



2. Twenty-two species of fish are listed from Douglas Lake, and detailed data on 

 their occurrence, weight, length, food, and interrelations are tabulated and discussed 

 (p. 229). 



