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 the animals and their habits would also be very useful; and 

 for any assistance given, acknowledgements will be made. 



The soft parts or "animal" of lo spinosa, Lea, or a description, would be a 

 desideratum. 



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

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



The 3d and 4th numbers of this work will most probably be devoted to the 

 genus Limnea, and will contain the following species. Those who are ac- 

 quainted with additional localities, will confer a favour by forwarding them 

 to the author. 



No. 3. — Limnea catascopmm. Hab. The North-west Territory, New York, 

 Massachusetts, the Hudson and Delaware. 



L. pinguis. The North-west Territory and the Delaware. 



L. emarginata. The North-west Territory and Maine. 



L. megasoma. The North-west Territory and Maine, 



L. rugosa. Mexico. 



L. jugularis. (Stagnalisl) Lewis' river, Oregon, and North-west Ter- 

 ritory. 



L. appressa. Superior, Canandaigua, and Cayuga Lakes; Vermont, Ohio, 

 and Indiana. 



No. A.— Limnea elodes. Hab. The Nort h-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 York, Ohio, Indiana, and Illinois. 



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

 and New England. 



L. aUcnuata. Near the city of Mexico. 



L. ezpansa. Vermont. 



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



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



