THE NAUTILUS. 131 



The study of this lake region was carried on under the 

 auspices of the Wisconsin Geological and Natural History Sur- 

 vey as part of a wide field study to ascertain the distribution of 

 the molluscan fauna of the State, preliminary to the prepara- 

 tion of a monograph of the aquatic species. An extensive 

 paper is in preparation covering in detail the ecological features 

 of the Winnebago fauna, both molluscan and general inverte- 

 brate, in which all of the molluscan species are discussed. 

 This will be published in the Transactions of the Wisconsin 

 Academy of Sciences, Art and Letters. Only new forms and 

 the more interesting new records are discussed in this paper. 



Truncilla triquetra Raf. A single specimen of this Truncilla 

 was dredged at Omro, Fox River, from gravel bottom, at a depth 

 of 8^ feet. This is a young shell, measuring, length 23, height 

 17, width 12 mm. Triquetra has not heretofore been reported 

 from Wisconsin and its presence in the Fox River is surprising. 

 It is known from southern Michigan and from Will County, 

 Illinois. The specimen was living when dredged. 



Lampsilis recta (Lamarck). Lakes Winnebago and Butte des 

 Morts. The recta inhabiting the lakes are uniformly smaller 

 than individuals living in Fox River. The relative difference 

 is shown in the table below in which the largest lake shells are 

 measured: 



Length 115, height 50, width 36 mm. Male, Doemel Point, 

 Lake Winnebago. 



Length 121, height 52, width 34 mm. Female, Long Point, 

 Lake Winnebago. 



Length 138, height 62, width 41 mm. Male, Princeton, Fox 

 River. 



Length 135, height 59, width 39 mm. Female, Princeton. 



This is a dwarf form produced by lake conditions and is par- 

 alleled by Lampsilis ventricosa canadensis and L. luteola rosacea. 

 The Winnebago shells are somewhat different from the Lake 

 Erie form named recta by Lamarck, the posterior ridge not be- 

 ing as well marked, but they seem clearly referable to the same 

 type. They are different from the ordinary river form of recta 

 (latissima} which is abundant in Wisconsin. 



Lampsilis gracilis lacustris n. var. Lakes Winnebago and 



