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wide geographic distribiuion over the northern United States, a fact which goes a 

 long way, first, in establishing their high antiquity as species, and second, the 

 fact that they have successfully adapted themselves to conditions which are widely 

 variant. Many of them occur far to the southward, beyond the limits of glacia- 

 tion, extending even to the middle portions of Alabama, some of them under 

 other names than those which we are accustomed to apply to them here. Dif- 

 ferences of a trivial character, the result of environment, appear to have been 

 seized upon by the species makers and the older naturalists whose ambitions alike 

 seemed to have been to write " nobis " after a specific name. 



REGISTER OF GENKRALLY DISTRIBUTED SPECIES. 



Unio claims. 

 * Unio iris. 



Unio luteolus. 



Unio ligamentintis. 



Unio multiradiatus. 



Unio rubiginosus. 

 ^Margaritana marginata. 



Anodonta ferussaciana. 

 ^Anodonta gi-andis. 



Sphaerium striatinum. 



Amnieola porata. 



Limnophyaa patustris. 



Limnophysa desidiosa. 



Physa heteroMropha. 



Unio ellipsi". 



Unia preii-ns. 



Unio gibbo.'ms. 



Unio rectus. 



Unio occidens. 

 Margaritana calceola. 

 Margaritana rugosa. 

 Anodonta edentula. 

 Sphaerium solidulum. 

 ■Sphaerium transveisum. 

 Amnieola Imiosa. 

 Limnophysa reflexa. 

 Helisoma trirotvis. 

 Physa gyrina. 



Goniobasis pulchella. 

 Summarizing this group of names, there are nine genera and twenty-nine spe- 

 cies; of these four genera and twenty species are bivalves; the rest are univalves. 

 There have been found up to this time, and thus certainly known to belong to 

 the Indiana fauna, a total of one hundred and sixty-five species of fresh water 

 shells. Nearly one-sixth, therefore, of our species are to be found all over the 

 State; this proportion will certainly be increased on thorough exploration. Geo- 

 graphic series, which have been studied, of these widely distributed forms show 

 some interesting facts in the line of variation, facts which are, most certainly, to 

 be correlated with peculiarities of environment. This is especially true of those 

 forms which are indifferently found in lakes, ponds or flowing streams, such as 



*These form? have been found in all but one ba-in in Indiana, with every probability 

 that each occurs therein and will be found on full exidoration. 



