The American Naturalist. 



[May, 



and Mohawk Rivers into the Hudson, and across into Lake 

 Champlain ; or they may have gone down the St. Lawrence 

 and up the Sorel. If by a subsidence since that time Lake 

 Champlain has been connected with the ocean, as is now be- 

 lieved, the Naiads of that lake no doubt retreated up the small 

 streams flowing into it, and returned after the elevation of the 

 land when its waters again became fresh. 



I think I am not making too sweeping an assertion when I 

 say that all the Mississippi Valley species of Naiades that have 

 entered the St. Lawrence, or in fact any part of the Atlantic 

 drainage areas, have become changed in some of their charac- 

 ters. As a rule, though not in every case, they have become 

 smaller, and simpler in their outlines ; the sculpture is less 

 pronounced or is almost obliterated ; in many cases the shells 

 are thinner, the nacre has lost its brilliancy, and instead of the 

 bright epidermis, often painted beautifully with rays or a 

 wonderful pattern of rich greens, yellows, and olives we have 

 mostly dull, livid, ashy or rusty reddish or brownish exteriors, 

 and they are very often somewhat distorted. This is not, as I 

 believe, in any great measure due to climate or colder water, 

 for these same species are as vigorous and finely developed in 

 parts of Wisconsin drained into the Mississippi, Minnesota 

 and Dakota as in any part of their area ; besides Anodonta 

 edentula under the name of A. undulata, and Unio (Margarita- 

 na) marginata when found in Maryland, Virginia, and probably 

 even south of that are so dwarfed and stunted as to be 

 scarcely recognizable. This changing of characters has been 

 well illustrated in a lot of Unionidse recently submitted to me 

 for examination by Prof. B. W. Everman of the U. S. Fish 

 Commission, which was collected mostly from the Maumee 

 basin by Dr. Philip H. Kirsch, of Columbia City, Indiana. 

 This region lies in Lat. 41° to 41^°, the most southerly part of 

 the St. Lawrence drainage. Unio. luteolus Lam., U. subrostratus 

 Say, U. circulus Lea, U. phaseolus Hild., U. multiplicatus Lea, 

 U. multiradiatus Lea, and Anodonta grandis Say, are so dwarfed 

 and stunted, and changed in color as to be scarcely recogniz- 

 able, while the same species from the Wabash, from which 

 these have no doubt all been derived, are as vigorous and 

 finely developed as any in the Mississippi Valley. 



