130 THE NAUTILUS. 



NEW SPECIES AND VARIETIES OF MOLLTJSCA FROM LAKE WINNEBAGO, 

 WISCONSIN, WITH NEW KECOKDS FROM THIS STATE * 



BY FRANK C. BAKER 



Winnebago Lake is the largest inland body of fresh water in 

 eastern America as it is also the shallowest in relation to its area. 

 Its greatest length is about 28 miles, its greatest width about 10 

 miles, and its maximum depth 20f feet. The lake is fed by 

 several large streams, Wolf River emptying into Lake Poygon 

 and Fox River entering Lake Butte des Morts. Lakes Butte 

 des Morts, Poygon, and Winneconne extend to the west of Lake 

 Winnebago and are marsh-bordered bodies of water. Butte des 

 Morts has a maximum depth of 15 feet, as has also the lower 

 part of the Fox River. All of these lakes are really widened- 

 out parts of the Fox and Wolf rivers, which encountered these 

 shallow basins when the ice receded to the north during the 

 waning of the Wisconsin ice cap. 



The Lake Winnebago region offers unusual opportunities for 

 the study of ecological variation. The Fox River, which flows 

 for many miles as a typical river, expands to form Lake Butte 

 des Morts, then narrows to form another river, which at Osh- 

 kosh again widens into the great body of water known as Lake 

 Winnebago; from this lake a river flows, the lower Fox, which 

 empties into Green Bay of Lake Michigan. The river, both 

 above and below the lakes, contains a typical river fauna of 

 mollusks. The lake fauna, however, although but a continua- 

 tion of the Fox River, it is not like the river fauna, the species 

 being smaller and otherwise differing from the typical river 

 species. This variation was almost universally noted among 

 the naides, the lake shells being easily distinguished from the 

 river shells. The gastropods also varied in like manner. The 

 fauna reached its present location by way of the Wisconsin-Fox 

 valley, following the retreat of the continental ice cap, and the 

 varieties in Lake Winnebago and Lake Butte des Morts were 

 probably evolved subsequently. 



* Contribution from the Museum of Natural History, University of 

 Illinois, No. 21. 



