56 Natural History Bulletin. 



THE MOLLUSCA OF EASTERN IOWA. 



By B. SHIMEK. 



The following list of the Molliisca of Eastern Iowa, though 

 incomplete, is offered as the result of observations continued 

 for a number of years. Many of our Mollusca are restricted 

 to very small and often obscure areas in their distribution and 

 consequently, unless a most searching investigation is made, 

 some will pass unobserved. Such an investigation has not 

 been made in this state except in limited localities and no 

 doubt many species exist which have not yet been reported. 

 This applies more particularly to the northern and western 

 portions of the state, the waters of which teem with moUus- 

 can life which is as yet imperfectly known. It was the wri- 

 ter's intention to spend the past summer in these portions of 

 the state, but no time could be spared and he was reluctantly 

 compelled to postpone this study. For this reason the follow- 

 ing notes apply more particularly to the molluscan fauna of 

 the eastern half of the state, though occasional references are 

 made to forms from other portions. 



The classification employed is in the main that of Tryon's 

 ^'■Structural and Sys^teniatic Conchology?^ While portions of 

 this may be objectionable it is well to remember that classifi- 

 cations usually change much more rapidly than do the charac- 

 ters on which they are founded, and if we thoroughly under- 

 stand the latter we ar^ prepared for a grouping of these char- 

 acters as employed in any classification. 



While great care was exercised in the following in exclud- 

 ing species of doubtful standing it is very probable that some 

 of those which are listed are mere varieties, but a much more 

 thorough study of them will have to be made before this can 

 be satisfactoril}^ determined. 



The genera Amnicola, Campeloma^Snccinea^ Liinncea, Plan- 

 orbis, Physa, Sphaerium, Pisidhtm, and Anodonta are par- 

 ticularly difTicult, and the final decision in many of these must 



