A REVISION OF THE LIMNAEAS OF NORTHERN 



ILLINOIS.* 



Frank Collins Baker. 



In the number of the Nautilus of June last the writer pre- 

 sented a revision of the Physae of the northeastern part of 

 Illinois, and in the present paper the genus Limnaea is dis- 

 cussed in the same manner. The Limnaeids seem to be 

 better understood than the Physae, although far too many 

 names have been given to them, founded for the most part 

 on very trivial characters. 



The collection of Limnaea in the Chicago Academy of Sci 

 ences is very rich, especially in the fauna of the Mississippi 

 Valley, and enough material has been at hand to satisfactorily 

 determine the specific standing of a number of names. The 

 writer may be thought to have been too radical in the matter 

 of synonymy, but the conclusions reached seem to be borne 

 out by the natural divisions of the group. 



My thanks are due to the following persons, either for 

 specimens, notes or suggestions: Mr. Bryant Walker, De- 

 troit, Michigan; Mr. J. H. Handwerk, Joliet, Illinois; 

 Messrs. T. Jensen, F. M. Woodruff, and Prof. W. K. Higley, 

 of Chicago ; and to the Natural History Survey of the Chicago 

 Academy of Science for the loan of the cuts in the text of 

 the present article. 



KEY TO SPECIES OF LIMNAEA. 



A. Shell 60 to 60 mill, in length. 



a. Aperture and spire about equal in length, the former much 



expanded. stagnalis. 



B. Shell 30 to 40 mill, in length. 



a. Spire attenuated, lonaer than aperture, the latter strongly 



reflexed; surface very rarely malleated. reflexa, 



b. Spire and aperture about equal in length; surface nearly 



always heavily malleated; shell wider in proportion to 



length than (a). palustris. 



* Presented, and read by title, before The Academy of Science of St. Louis, 

 December 17, 1900. 



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