140 



It was fiiitluT discoveroil that as the Ohio River forms of Cnia are traced 

 over the regions southwards and tlieir geographic and geologic environment be- 

 comes clianged, that a large iiund)er of them sensil)ly change tlieir external par- 

 ticular characters and grade into forms to this time regarded as peiuiliar to the re- 

 gion. At once here was opened up the great (|uestion of synonymy, with all the 

 consequences which are involved in a wholesale reduction of species. 



This study, then, in its final form, will seek to investigate the synonymy — 

 First, of tlie shells which have been described from the Ohio Kiver. Second, it 

 will select the mos-t marked species of these river mussels and about them, as 

 types, attempt a natural groujiing of the Tnioninc fauna of the valley and tlie 

 region south. Third, it will attenipt to eliminate the synonyms which have been 

 so multiplied by earlier students who were misled by inadequate data or by the 

 older notions of what constituted a species. It will, further, explaiii in a measure 

 the way in which the different forms assumed by the sexes came to 1)C regarded as 

 sjiecies — an unfortunate condition which the dilettante of the present day are mak- 

 ing worse. It will, fifth, seek to collect, for convenient reference, all figures and 

 descriptions, in the hope that in this way the historic importance of the earlier 

 descrii)tions may become apparent. These will be arranged chronologically. The 

 Ohio River constitutes historic conchologic ground; from it must begin, as began 

 tiie old, tiic new stndv of the Unianidd'. 



Thk Strepomatid.k of the Falls ok thk Ohio. Ev R. Ellsworth Call. 



[AlSSTRACT.l 



The Strepomatid molluscaii faitna of the Falls of the Ohio is one that is very 

 rich in numbers, but rather poor in species. Including some which will eventu- 

 ally pass into synonymic lists, the total number comprizes but ten species which 

 are distributed among four genera, to wit: Pleurocera with three nominal s])ecie.s, 

 Lithasia with one species, ^iiiruloxa with two species, and (loiiiobdsls with four 

 species. 



The falls mark the line of junction of the Silurian and Devonian strata, 

 which may here be differentiated with very great success and ease. For a distance 

 of some five or six miles the bed of the river is very rocky, with numerous islets 

 of rock, whit'h are always exposed at low water. l"''rom one end to the other are 

 innumerable pools in which flourishes a very rich ron/ervoid flora, and which furn- 

 nisli a very variable but favorable station for these forms. In numerous places 

 'the changes in the current arc so marked that at difTerent seasons of the year the 



