18 96.] On the Mississippi Valley Unionidce. 383 



This great change in size, form and coloring has caused stu- 

 dents to bestow many specific names on what I believe are 

 merely northern races or varieties of common Mississippi Val- 

 ley species. Thus Anthony's Anodonta subangulata and Lea's, A. 

 Jootiana, A. marryattana and A. benedictii are merely dwarfed and 

 slightly changed forms of Say's, A. grandis. Anthony's A. 

 subinflata is probably a form of A. corpulcnta Cooper, and A. 

 mbcylindracea Lea, is the northern manifestation of Lea's well 

 known A. ferussaeiana. Say's Anodonta edentula becomes in 

 Michigan Alasmodonta rhombica of Anthony, and further east 

 and southeast A. undulata of Say ; Lea's Unio circulus of the 

 central Mississippi area changes in Lake Erie to the dwarf 

 U. leibi of the same author ; his U. canadensis is only an altered 

 over U. ventricosus of the western States, and A. Gray's U. 

 borealis is a very much changed form of the common U. 

 luteolus, while U. hippopseus Lea, of Lake Erie is, I believe, 

 only a stunted U. plicatus that has almost entirely lost its pli- 

 cations, and has assumed a dirty, reddish or olive color. 



Some of these are possibly valid species; most of them 

 would certainly be considered so, together with a number of 

 other northern manifestations of Mississippi Valley species 

 were it not that so many intermediate links are found. 



It sometimes happens that specimens of a given species are 

 found in the Mississippi area, growing, no doubt, under un- 

 favorable conditions, that so closely imitate the same species 

 found in northern waters as to be indistinguishable from it. 

 Thus Lea has in his collection what he called Anodonta 

 Jootiana, a Michigan form, from Illinois, and depauperate Unio 

 plicatus are sometimes found in the Mississippi area that are 

 almost exactly like U. hippopseus. And on the other hand 

 occasionally fine specimens of Unio rectus, U. rubiginosus, 

 Anodonta ferussaeiana and A. grandis are found in the St. Law- 

 rence drainage that are perfectly normal. Yet as a rule 

 an expert can tell at a glance whether a specimen grew in the 

 Mississippi area or was extra-limital. 



Anodonta simpsoniana Lea, is, I believe, a good species, 

 although it is probably an altered and dwarfed A. grandis. 



