ORTMANN: monograph of the naiades of PENNSYLVANIA. 229 



In the tributaries of the Ohio in West Virginia it appears to be the rule that 

 levigata is the form of the smaller streams. In Ohio aside from the Mahoning 

 River (Dean) this form is positively known to occur in the Tuscarawas River 

 (Dean, 1890, also Carnegie Museum), and it has been reported from the upper 

 Scioto, Columbus, Franklin Co. (Lea), and it has crossed over into the lake-drainage 

 (St. Joseph River) . 



Further, Call (1885) cites it from Tennessee in Elk River, Lincoln Co., but 

 says that it is identical with "circulus." That it is actually there, a little farther up, 

 is shown by specimens in the Carnegie Museum. It also is found in a number 

 of the tributaries of the Tennessee in northern Alabama and northern Georgia, 

 and has been detected in the Holston above Knoxville (very rare at this point). 



Ecologically this form is in Pennsylvania and West Virginia distinctly sand- 

 loving. It is found in bars of sand or fine gravel, and is even not averse to shifting 

 sand. 



Subgenus Pseudoon Simpson (1900). 

 Ortmann, 1912, p. 321; Simpson, 1914, p. 298. 



Type Amblema olivaria Rafinesque. 

 Only one species is found in Pennsylvania. 



Obovaria (Pseudoon) olivaria (Rafinesque) (1820). 

 Ohovaria ellipsis (Lea) Simpson, 1914, p. 299; Obovaria olivaria (Rafinesque) 

 Vanatta, 1915, p. 553. 



Plate XIII, figs. 8, 9. 

 Records from Pennsylvania: 



Stupakoff, 1894 (Allegheny Co.). 

 Ortmann, 19096, p. 192. 



Characters of the shell: Shell of medium size, thick and solid. Outline elliptical 

 or subovate, longer than high, strongly oblique. Anterior and lower margins 

 forming a regular curve, the lower margin curving up behind, and joining the pos- 

 terior margin in a curve, without forming an angle, but posterior end of shell more 

 narrowly rounded than' the anterior. Upper margin convex, passing gradually 

 into the descending posterior margin. Beaks swollen, directed obliquely forwards, 

 incurved, and located much anteriorly, but generally a little behind the most 

 anterior part of the anterior margin, elevated somewhat above the hinge-line. 

 Beak-sculpture rudimentary, consisting of four or five fine bars, which are sinuate 

 in the middle. The posterior part of the bars is rudimentary and disappears upon 



