284 ORTMANN— CORRELATION OF SHAPE AND 



Loc. No. 



Little Kanawha River, Burnsville. 12 



Raccoon Creek, New Sheffield ... 9 



Chartiers Creek, Carnegie 3 



Since the compressed form of the headwaters (flava) very 

 gradually passes into the more swollen form of the larger rivers 

 (trigona) , the distinguishing line between them necessarily must be 

 arbitrary. I have adopted 55 per cent, as the limit, so that shells 

 with the diameter of 55 per cent, and over are called trigona, while 

 shells with less than 55 per cent, are flava. 



Group of Fusconaia cuneolus in the Upper Tennessee- 

 system. 



Fusconaia flava and trigona are absent in the upper Tennessee- 

 drainage, but they are represented there by two allied species, which 

 agree in general shape and in anatomy with the Ohio shells, but 

 differ from them, and from each other, chiefly in the color of the 

 epidermis. They appear to be good species, for they do not run 

 into the flaz^a-iype anywhere, and I also have never found evidence 

 that they run into each other. These shells are F. cuneolus and F. 

 cdgariana. In both of them, however, the same phenomenon as 

 regards obesity is observed. 



F. cuneolus has the following forms and synonyms.^* 



1. Fusconaia cuneolus (Lea). — Dia. less than 50 per cent. 

 Unio cuneolus Lea, '40 (Holston R.). — Pleurobema cuneolus Simp- 

 son, '14, p. 743. 



Dia (Lea) : 43 per cent.; (Simpson) : 42 and 46 per cent. 



2. Fusconaia cuneolus appressa (Lea.) — Dia. 50 per cent, 

 or over. 



Unio appressus Lea, '71 (Tennesse R., Tuscumbia ; Holston R.). — 

 Pleurobema appressa Simpson, '00, p. 749. 

 Dia. (Lea) : 52 per cent. 



Unio tuscumbiensis Lea, '71 (Tuscumbia; Holston R.). — Pleuro- 

 bema tuscumbiensis Simpson, 14, p. 748. 

 Dia. (Lea) : 56 per cent.; (Simpson) : 56 and 58 per cent. 



" See Pr. Amer. Philos. Soc, 57, '18, pp. 530, 53i- 



