ORTMANN: monograph of the naiades of PENNSYLVANIA. i 



Shell with sculpfurc upon the disk (ridgos or tubercles). Bcak-sculpturc concentric, 

 dc)uble-l()()]MHl or zig-zag. 



Ci. Cliief sculpture upon disk consisting of a few oblique, strong undulations. Beak-sculpture 

 concentric A mblcma. 



Ci. Cliief sculpture on disk consisting of tubercles and warts. Beak-sculpture concentric, 



double-looped, or zig-zag Quadrula. 



tti. Only the two outer gills serving as marsupia. 

 61. Shell more or loss tubercular upon the disk. 



C\. Beak-sculpture well-developed, consisting of numerous wavy ridges. Nacre dark purplish. 

 Soft parts whitish. No supra-anal Rolundaria. 



Ci. Beak-sculpture rudimentary, consisting of a few obscure, concentric bars. Nacre light- 

 colored. Soft parts generally pale orange. Supra-anal present Plethobasus. 



6 J. Shell smooth upon disk, without tubercles. 



Ci. Shell rather thick and solid, short and high, sometimes drawn out posteriorly, and then 

 distinctly cuneiform and oblique Pleurobema. 



Co. Shell generally not very thick, often rather thin, not short and high, but more or less elon- 

 gated, and not oblique Elliptio. 



Genus Fusconaia Simpson (1900). 

 Ortmann, 1912, p. 240; Simpson, 1914, p. 865 (as section of Quadrula). 



Type Unto trigonus Lea {= F. flava trigona) . 



Key to the Species and Varieties. 

 Oi. Shell without a distinct posterior ridge, disk rather uniformly convex. Color brownish, or blackish 

 brown. 



61. Diameter of shell fifty percent of length, or more F. subroiunda. 



62. Diameter of shell less than fifty percent of length F. subrotunda kirtlandiana. 



ao. Shell with a distinct posterior ridge, disk flattened, or even slightly concave in front of the ridge. 



Color lighter, more reddish or yellowish brown. 

 61. Shell attaining a good size. Growth-lines irregular. 



Ci. Diameter of shell less than fifty-five percent of length F. flava. 



C2. Diameter of shell fifty-five percent of length or more F. flava trigona. 



bi. Shell much smaller. Diameter very variable, but mostly considerable. Growth-lines very 

 distinct and regular F. flava parvula. 



Fusconaia subrotunda (Lea) (1831).* 

 Quadrula subrotunda (Lea) Simpson, 1914, p. 892. 



Plate I, fig. 2. 

 Records from Pennsylvania: 



Harn, 1891, p. 137 (western Pennsylvania). 



Clapp, 1895, p. 116 {U. pilarLs from Allegheny County is undoubtedly this). 



8 This should not be called F. sintoxia (Rafinesque), although Vanatta (1915, p. 5.5S) identifies 

 Rafinesque's species with it. According to the measurements given l)y \'anatta, the diameter of Rafines- 

 que's sintoxia is forty-three percent of the length; and tiuis it could only fall umler kirtlandiana. But 

 since the nacre is described as rose-colored, this does not seem likely since subrotuiidn and kirtlandiana 

 have not rose-colored nacre. 



