CIRCULAR. 



It is intended that this work shall embrace all our species hitherto described 

 by American and European authors; and as the geographical distribution is 

 a matter of great importance, and one which has not been sufficiently noted, 

 the author will be greatly indebted to those who take an interest in this sub- 

 ject, if they will forward him catalogues of the species, or specimens of the 

 univalve shells found in the streams with which they may be acquainted. 



Descriptions of tne animals and their habits would also be very useful; and 

 for any assistance given, acknowledgements will be made. 



Communications may be addressed to the author, at Marietta or Columbia, 

 Pennsylvania, or to the care of Mr. DOBSON, Philadelphia. 



No. 4.Limnea elodes. HAB. The North-west Territory, Lake Erie, New 

 York, Eastern Pennsylvania and Massachusetts. 



L. umbrosa. Council Bluff; Rainy lake and Seine river of Upper Canada; 

 New England, New Fork, Ohio, Indiana, and Illinois. 



L. refiexa. Superior and Erie lakes; Ohio, Indiana? Illinois, New York, 

 and New England. 



L. attenuata. Near the city of Mexico. 



L. expansa. Vermont. 



L. desidiosa. New England, New York, Pennsylvania, and Ohio. 



L. caperata. Illinois, Indiana, Ohio, E. Pennsylvania and Vermont. 



CORRECTIONS. 



Paludina Bengalensis. Add to the synonyms 



P. VITTJLA, Raf. Atlantic Journal, p. 165. 



No. 2, p. 21, line 11, for worst read worse. 



Paludina subpurpurea. In some copies the bands are too highly colored. 



Physa osculans. The U. S. specimens of this shell will merge into P. 

 heterostropha. One specimen, supposed to be from the West, is in reality from 

 Mexico. This appears distinct, and may retain the name, until I learn more 

 about it. Although the aperture is narrow, some specimens in the Academy's 

 collection have it very wide. 



*** This number has been detained by extensive alterations in the plates, 

 after the engraving had been finished. This explanation is made to allay the 

 fears of those subscribers who may suppose the work likely to be discontinued: 

 a circumstance of which there is no apparent probability. 



