UNIO INTERRUPTUS. 



SPECIFIC CHARACTER. 



An elevated umbonial slope, separating folds of the disk 

 from folds of the anterior margin. 



SYNONYM. 



U. INTERRUPTUS, Nob. Tmnsijlvania Journal^ Vol 4, 

 p. 525. 



DESCRIPTION. 



Shell transversely oblong oval or subrhomboidal, black- 

 ish brown ; an elevated rib extends from the apex to the 

 anterior basal angle along the umbonial slope ; anterior 

 half of the disk with somewhat oblique undulations ex- 

 tending nearly to the umbonial rib ; anterior to the umbo- 

 nial rib are several arquated undulations, which do not 

 reach the edge of the shell, and are cut by an impressed 

 line which is nearly parallel to the rib : i«y»^o compressed : 

 beaks not elevated, deeply eroded : posterior margin very 

 short, rounded : ligament margin rectilinear, the anterior 

 angle elevated, obtuse ; anterior slope very oblique: base 

 rectilinear, parallel to the ligament margin ; anterior ba- 

 sal angle somewhat rostrated: cavity of the hinge mem- 

 branes (or excavated lunule) fusiform : within purplish, 

 iridescent: cardinal teeth direct, deeply granulated and 



PI. 33. 



