Synopsis Fresh-Water Mollusca 



47 



Genus AMBLEMA Rafinesque, 1819. 



■ Shell more or less alate ; beaks prominent, sculptured with coarse, con- 

 centric or somewhat double-looped ridges which do not extend over the 

 surface of the shell; surface of the valves usually sculptured with oblique 

 folds; posterior slope generally having small radial plications, which curve 



Fig. 150 



upwards behind ; epidermis brownish or blackish ; anterior muscle scars 

 large, distinct, very shallow, the anterior edge smooth, the rest apparently 

 filled with roughened shelly matter; posterior scars large, shallow, indis- 

 tinct; escutcheon large and dark. 



iVtarsupium occupying all four gills. 



-^, an 



Fig- 151 

 Type: A. costata Raf. 



Example: A. iindnlata (Bar.), fig. 150. Animal, A. trape::oides (Lea), 

 fig- 151- 



