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 Gontobasis, 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 
albinos}, 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. Pisidium 
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 Unionide, and possibly more), while at least two or 
three of them are widely distributed over the state. 
+ 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. 
