Family UNIONIDAE 



Valves nacreous; siphons short; usually with pseudocardinal 

 teeth and with lateral teeth posterior to them, sometimes absent; 

 with a glochidial larval stage, usually parasitic on fishes 



Subfamily MARGARITANINAE 



Gills without water tubes and with only scattered inter- 

 lamellar connections; shell long and usually arcuate; later- 

 al teeth very blurred (Sometimes grouped as a separate 

 family) 

 Common genera — Margaritana Cumherlayidia 



Subfamily ANODONTINAE 



Gills crosswise divided into water tubes; water tubes of 

 gravid female lengthwise divided into three sections or 

 tubes, with the middle ones serving as ovisacs to form the 

 marsupium, which extends the length of each outer gill; 

 hinge teeth reduced or absent 

 Common genera — Anodonta Arcidens 



Strophitus Ar}{ansia 



Alasynidoyita Lasmigona 



Decuramhis Simpsoniconcha 



Pegias 



Subfamily UNIONINAE 



Water tubes of gravid female undivided; marsupium 

 sharp-edged, formed from all four gills or from the outer 

 gill on each side; hinge teeth usually complete; inter- 

 dentum usually flat; valves usually sculptured; no distinc- 

 tion between male and female shells 

 Common genera — Elliptio Ohliquaria 



Pleurohema Dromns 



Canthyna Cyprogema 



^uadrula Hemistena 



Amhlema Ptychohranchus 



Gonidea 



Subfamily LAMPSILINAE 



Water tubes of gravid female undivided; marsupium 

 swollen beyond the edge of the gills, usually formed only 

 from the posterior part of the outer gills; hinge teeth 

 usually complete; interdcntum usually rounded; valves 

 usually smooth; female shells often more swollen or some- 

 times more rugose posteriorly than the male 



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