Family Unionidae. Hinge with schizodont teeth; embryo a glochidium. 
Subf amily Unioriinae. Beak sculpture concentric; embryos in outer or all four of the gills. (Exo branch i a e.) 
Ovisacs not separa ted by a sulcus. Ovisacs distinctly marked out by a sulcus. 
Male and female shells alike. 
39 
(M e s 0 g e n a e.) 
Marsupium a few ovisacs in the 
center of outer gills. 
(P t y ch 0 g e n a e.) 
Marsupium occupying the whole 
outer gills in a series of folds. 
iCyprogenia Agassiz. 
lObliquaria Rafinesque. 
Ptychobranchus Simpson. 
(E s c h a t i g e n a e.) Dr om us Simpson. 
Marsupium occupying the outer 
border of outer gills. 
(D i a g e n a e.) 
Ovisacs filling the outer gills, 
running crosswise. 
(Ho mo g e n a e.) 
Marsupium filling the entire outer 
gills and forming smooth pads. 
Strophitus Rafinesque. 
A nod on ta Bruguière. 
Colle to pterum Bourguignat. 
Gabillotia Servain, 
Leguminaia Conrad. 
Lastena Rafinesque. 
Sol en ai a Conrad. 
Gonidea Conrad. 
I Anodontoides Simpson. 
^ P egias Simpson. 
Ar ci de ns Simpson. 
Symphinota Lea. 
lAlasmidonta Say. 
[Hemilastena Agassiz. 
Mar gar it ana Schumacher. 
I U n X 0 Retzius. 
^Pleurobema Rafinesque. 
(T e t r a g e n a e.) 
Marsupium filling all four gills, 
forming smooth pads ; bleak cavities 
deep. 
(Quadrula Rafinesque. 
I Schistodesma Simpson. 
^Gibbosula Simpson. 
ICuneopsis Simpson. 
