ORTMANN: monograph of the naiades of PENNSYLVANIA. 207 



ci. Placentae moderately long, slightly curved. Marsupium just behind the middle of the gill. 



Outside of shell with a few large knobs Obliquaria. 



Ci. Placentae very long, spirally coiled up. Marsupium in, or slightly in front of, the middle of 



the gill. Outside of shell with numerous small tubercles Cyprogenia. 



ai. Marsupium kidney-shaped. Ovisacs lanceolate, dilated and compressed. Placenta; not very .solid. 



Inner edge of mantle in front of branchial opening, more or less differentiated. Shell rouiulod, 



elliptical, or elongate, without sculpture on the disk. 



hi. Inner edge of mantle, in front of branchial opening, slightly lamellate and crenulated, but without 



papillae or flaps. Male and female shell differing only slightly in shape, or hardly at all. 



C\. Shell rounded, ovate, or subelliptical. Glocliidia of normal size and shape, subovate. 



di. Shell rounded or short-ovate. Epidermis brownish, rarely greenish, with indistinct 



rays Ohovaria. 



^2. Shell ovate or subelliptical, elongate. Epidermis greenish or yellowish, with more or 



less distinct rays Actinonaias. 



Co. Shell ovate, triangular, or subelliptical. Glochidia either of abnormal size or shape. 

 di. Shell subovate or subtriangular, with a strong posterior ridge. 



ei. Glochidia of normal shape (subovate), but of abnormally small size. Shell sub- 

 ovate or elongate Amygdalonaias. 



Co. Glochidia spatulate, with gaping margins, very large. Shell subtriangular. 



Plagiola. 

 do. Shell subovate or subelliptical, generally compressed and winged at the upper posterior 

 part, without distinct posterior ridge. 

 ei. Glochidia of normal shape, but of abnormally small size. Shell rather thin. 



Paraptera. 



62. Glocliidia celt-shaped, with two spines on each valve. Shell tliicker Proptera. 



bn. Inner edge of mantle, in front of branchial opening, with papillte or flaps. Male and female 

 shell distinctly, and often greatly, different in shape. 

 Ci. Inner edge of mantle parallel with and close to the outer edge. Glochidia subovate or 

 subelliptical. 

 di. Inner edge of mantle with papiUse. 



ei. Papillae few, represented chiefly by one large caruncle. Shell very small. Beak- 

 sculpture concentric Toxolasma. 



62. Papillae more numerous. Shell smaU, medium, or large. Beak-sculpture double- 

 looped Eurynia. 



di. Inner edge of mantle forming a ribbon-like flap, projecting at the anterior end. Shell 



large Lampsilis. 



Co. Inner edge of mantle, in front of branchial opening, more or less remote from outer edge in 

 the feinale. Glochidia subcircular. Shell rather small, of peculiar and various shapes, 

 cliiefly in the female Truncilla. 



Genus Ellipsaria Rafinesque (1820). 

 Ptychohrancus (Simpson) Ortmann, 1912, p. 305; Simpson, 1914, p. 332; Ellip- 

 saria Frierson, 1914a, p. 7. 



Type Obliquaria fasciolaris Rafinesque. 

 Only the type-species known from Pennsylvania. 



