322 Cincinnati Society of Natural History. 



which seems to me to have a much greater sig-nificance than is to be 

 attached to merel\' local causes, or those of present or comparative!}^ 

 recent action. 



We may now pass to the consideration of streams outside of the 

 Ohio and Mississippi drainage, and among these the most anomalous 

 is the Alabama, from whose prolific waters 184 species have been de- 

 scribed, not half of which are more than the merest varieties. 



But here we meet with two genera, not yet found elsewhere, and em- 

 bracing a list of about 30 described species. If this fact stood alone, 

 we might not regard it as exceedingly anomalous; but witli it is the 

 testimony that these two genera, Schizo^toma and Tidotoma, as well as 

 the peculiar species of Goniobasis associated with them, belong to a 

 fauna of separate origin from many of the Unionidce found as their 

 associates in the same stream. I am well aware of the fact that this 

 statement rests upon synonymy which some American students of 

 Coosa and Alabama river shells do not recognize; but it is nevertheless 

 true, that a large number of species belonging to the Ohio drainage 

 have their varietal forms in .the Gulf system of Alabama, almost as 

 plainl}^ indicated as in that portion which belongs to Texas'. The 

 species from Florida are different, and no Ohio river type exists there. 

 When we consider the shells of the Atlantic slope, though a large num- 

 ber of species has been made of them, it is not difficult to demon- 

 strate a ver}^ numerous list of svnon^^ms among the Unionidoi, until 

 we have reached the southern borders of North Carolina, where a new 

 fauna begins to appear, that culminates in Southern Georgia and 

 Florida, having a very marked series of Streponiatidoi, quite distinct 

 from the Ohio drainage by i-ts want of the genera Pleurocera and An- 

 ciilosa, and the introduction of many species of Unionidce not readily 

 referred to Ohio types. This region contains the U. spinosus Rlve^idy 

 mentioned, and a number of species fur removed from the ordinary 

 types of their genei'a, as the U. shepherdlanus and the Marg. arcula, etc. 



When the fresh-water shells of the west coast are examined, we 

 find the families under consideration to have but few species, and 

 these embracing some forms of very great distinctness, as the Anodouta 

 wahlamatensis, A. angulata, Goniobasis plicifera, and G. occata. 

 The only species of Margaritana is the M. margaritifera before men- 

 tioned. 



In summing up the facts which extensive collections of these shells 

 from authenticated localities set forth, one prominent one presents itself; 

 and that is, that man\^ of the species never present au}^ varietal difiTer- 



