APPENDIX. 425 



original views. Here again I am restrained as before, and shall not 

 enter into full details. I am of the opinion that Say's Melania armi- 

 gera is an lo. Beyond this, I am unprepared to admit more than one 

 species, though I am aware that others claim more on apparently good 

 grounds. The genus lo, as heretofore limited by yourself, is spread 

 out over the Ui^per Tennessee drainaye. It occurs in the principal 

 confluents that unite, forming the Tennessee River, above Chattanooga, 

 and a few specimens have also been found in that portion of the 

 Tennessee River that flows through Jackson County, Alabama. In 

 Clinch River, I have, by Miss Law's aid, obtained perhaps three well 

 marked varieties, one of which, certainly, most naturalists would call 

 a good species. In the Holston and Tennessee I also find varieties 

 one of which seems to have been derived from French Broad River, 

 where only a single form appears. You are aware that a smooth 

 variety (which I have not yet obtained) occurs in the Upper Holston, 

 and varies so much as to be regarded as two species, rollowing 

 Say's Melaiiia armi(iera through, its somewhat extensive distribution, 

 I find that it begins to appear where the conventional lo disappears, 

 and takes the place of "lo" in the Lower Tennessee River, Cumber- 

 land River, Wabash River, etc., etc. In the difl'erent stations where 

 found, it varies pretty nearly as the typical lo does. In some in- 

 stances it has varied so much as to have been redescribed as a distinct 

 species, and in one instance (one of my correspondents suggests) a 

 young shell was the occasion of the erection of a new genus. Now 

 taking the parallel between the typical lo and Say's armigcra, what 

 shall we do? Shall we admit all the species and genera proposed, or 

 will it suflice to write all there is of lo under two s\^i^c\cs, fluvialis and 

 armigera? And while we have before us this question of the vari- 

 ability of species, let us inquire how many species are there of Say's 

 Melania luipera? This species varies in difl'erent stations quite as 

 much as fluvialis and armigera. Specimens entirely smooth are not 

 rare. Others that are undulate contrast with the more numerous 

 nodulous specimens. Colors and bands ofi'er contrasts as in fluvialis 

 and armigera. Now does not analogy have some weight with us some- 

 times? But, if it does, can we say that we treat these things con- 

 sistently? 



Let us consider the univalves of the Alabama drainage, saj- of the 

 Black Warrior, Alabama, Coosa and Cahawba Rivers. I have tried to 

 identify these, or some of these univalves, with those of the Ten- 

 nessee drainage that circles through northern Alabama, and with the 

 one exception of a Melantho, which I believe you separate as a dis- 

 tinct species, I find nothing identical. Perhaps there may be some- 

 thing identical in Somatooyuus, but I have not had opportunity to 

 make satisfactory comparisons. This leads me to question your iden- 

 tification of Strephobasis Clarkii (of the Tennessee drainage) with S. 

 bit(vninta (of the Alabama drainage = Black Warrior River). 



I find evidence that leads me to unite T.annuliferum Viwd prasinatum. 



