ortmann: monograph of the naiades of Pennsylvania. 21 



the uppermost limit of its distribution in the Ohio system. It is remarkable 

 that I have not found this form or any representative of it in the Ohio in Beaver 

 County. Its absence in the lower Allegheny may be accounted for by the general 

 destruction of the molluscan fauna in these waters. Moreover F. flava irigona 

 probably is extinct in the state at the present time. The specimens collected by 

 myself at Neville Island were all dead, and there are no more shells at this locality, 

 nor at Rhoads' locality, Coraopolis. Ehrmann's collections in the Monongahela 

 were made before 1898, and most of his shells were found dead. 



General Distribution. Type locality: Ohio River, Cincinnati and Louisville 

 (Lea). 



The distribution of F. flava Irigona is very unsatisfactorily known. Walker 

 reports it from the Ohio, and it extends westward to the Mississippi at Davenport, 

 Iowa, and to the Wisconsin River, Sauk Co., Wisconsin (Walker). 



The Carnegie Museum possesses a number of specimens from the Kishwaukee 

 River, Rockford, Winnebago Co., Illinois (P. E. Nordgren), which in general 

 correspond with F. flava; but one among them, which is considerably swollen, 

 might very well be considered to belong to the variety trigona. These shells are 

 rather large, with blackish epidermis. The other localities mentioned above, are 

 rather isolated (in West Virginia, Indiana, Arkansas, Oklahoma, Louisiana), but 

 they tend to show that under certain conditions, the form flava undata passes, in 

 localities remote from each other, into a form with less elevated beaks, which 

 answers to the description of U. trigonus of Lea. What these conditions are, 

 remains to be seen. Possibly trigona is the form of medium-sized rivers with 

 strong currents. 



It is remarkable that I did not see a trace of this form on my collecting trips 

 down the Ohio between Pittsburgh and Cincinnati. The shell should be expected 

 in this region, but careful examination of the shell-heaps of the clam-diggers and 

 my own collecting did not bring to light a single specimen. Probably this form 

 selects particular stations in the river, but of what character these are, is as yet 

 unknown. At Neville Island in Pennsylvania, I found the dead shells in and above 

 riffles in a stoall branch of the Ohio, immediately below a rather long, quiet pool. 



, FuscoNAiA FLAVA PARvuLA Grier (1918). 



Unio rubiginosus Norris, 1902, p. 119 (Winona Lake); Quadnda rubiginosa 

 Ortmann, 19096, p. 203 (Lake Erie); Quadrula undata (pars) Walker, 

 19106; Quadnda undata (pars) Simpson, 1914, p. 880; Fusconaia flava parvula 

 Grier, 1918, p. 11. 



