ORTMANN: FAMILIES AND GENERA OF NAJADES. 305 
ci. Shell rounded, ovate, or subelliptical, without or with indistinct posterior 
ridge. Glochidia of normal size and shape, subovate. 
d,. Shell rounded or ovate, swollen. Epidermis brownish, rarely greenish, 
Valen, siaahGunics IghebcooeecapalaoouacecHoOnecCoaaUlé Obovaria. 
ds. Shell subovate or subelliptical, compressed, or only slightly swollen. 
Epidermis greenish or yellowish, with more or less distinct rays. 
Nephronajas. 
c.. Shell ovate, triangular, swollen, or subelliptical and compressed. Glo- 
chidia of abnormal size or shape. 
dy. Shell subovate or subtriangular, with a strong posterior ridge. 
e1. Glochidia of normal shape, but abnormally small size. Shell 
SuboOVvateronelongates. a-racitetas cles er cke cries Amygdalonajas. 
ex. Glochidia spatulate, with gaping margins, large. Shell sub- 
triam ouilary peer iacereta crerecclauere ero ahd wlio meus eh dorian cba Srelovs\eite ey Plagiola. 
d2. Shell subovate or subelliptical, more or less compressed, often winged, 
without distinct posterior ridge. 
e1. Glochidia of normal shape, but abnormally small. Shell rather 
(ELON ays aehete te sh ee dere he eta tee ld he aaa Cmte eA ae Paraptera. 
ex. Glochidia celt-shaped, with two spines on each valve. Shell thin 
OL rath erathi Ghent spacysty don sporte las erect orale stelefalorsc Proptera. 
bs. Inner edge of mantle with papillz 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. Shell 
ovate, elliptical, or elongated. Glochidia subovate. 
di. Inner edge of mantle with papille. 
e1. Shell with nodulous plications upon the posterior slope. 
Medionidus. 
exmsnelliwithoute Sculpture sarierciem cisetcisiotie: oii eter ete Eurynia. 
d». Inner edge of mantle forming a ribbon-like flap......... Lampsilis. 
co. Inner edge of mantle in front of the branchial opening more or less remote 
from outer edge in the female. Shell variable, not ovate or elliptical. 
Glochidiaalmostsemicirculatsaccrcciee cece iia cers oe Truncilla. 
In all these genera, we have a beak-sculpture, which is rather rudi- 
mentary, and, when developed, either of the concentric or the double- 
looped type. Beak-sculpture in this subfamily is apparently a char- 
acter becoming more or less obliterated, and thus cannot be used for 
general systematic purposes, although it is available as a subsidiary 
character in a few cases. 
Genus PTyCHOBRANCHUS Simpson. (1900.) 
(Simpson, 19000, p. 612.) 
Shell subelliptical, somewhat elongated. Disk smooth, sometimes 
with ridges on the posterior slope. Beak-sculpture indistinct, con- 
sisting of a few ridges, the first concentric, the others slightly double- 
