MOLLUSCA OF OHIO. 369 



unnecessary to cite numerous localities, except of such as are 

 comparatively little known. "Over the state" seemed sufficient, 

 even if such a species has actually been seen from few places. I 

 am well aware of the fact that some widely distributed, and 

 even generally common species, may be absent over stretches of 

 many miles, or in whole river systems, — if not simply overlooked. 

 To ascertain and register such gaps of distribution*, and also 

 their causes, may be possible when the whole territory is worked 

 up better than it is at the present time. On the other hand, it 

 seemed to be in place to add some notes on such species and 

 forms which are of special interest with respect to either their 

 systematic position, variation or distribution, things which 

 constitute the characteristic features of a local or state fauna. 



The list was intended to contain the species and varieties 

 known to occur in Ohio, and recognized as such, seen by myself 

 or cited on good authority. There are, however, a few excep- 

 tions, much to my regret. I am not familiar with many of the 

 Pleurocera and Goniobasis, and also with some Anodonta of the 

 St. Lawrence drainage. More material from all over the state, 

 and special study, will be necessary in order to ascertain which of 

 them represent valid species, varieties or local forms, and their 

 distribution. 



As varieties, I regard only such forms which, although 

 connected with the typical, somewhere, by intermediate spec- 

 imens (otherwise they would represent distinct species), main- 

 tain their characteristic features over a larger or smaller territory ; 

 in short, propagate as such. Individual variations, such as 

 albinosf, reversed (usually sinistrorse) specimens, and shells 

 with imperfectly or abnormally formed apertures, as occasionally 

 found with the normal forms, cannot be regarded as varieties, 

 in the accepted sense of the term. 



In regard to classification and nomenclature, I have fol- 

 lowed, for the most part, our leading conchologists. in some 

 instances contrary to my own views. A faunal list is not the 

 place for controversies on these topics. Where yet dissenting, I 

 believe to have good reasons, e. g., in adhering to Hyalina 

 instead of Vitrea, Patula instead of Pyramidula. Pisidiitm 

 versus Corneocyclas has been vindicated by higher authority 

 than myself. For recognizing Proptera as a genus, I have given 



* As an example of this kind, the fact may be cited that none of the 

 four species of Proptera has been found in the Tuscarawas River (with its 

 thirty-six species of Unionida\ and possibly more), while at least two or 

 three of them are widely distributed over the state. 



t Such are found especially of many species of Polygyra and Patula: 

 but I know of no instance where any of them are constant and conse- 

 quently constitute varieties. 



