Synopsis FrEsh-Water Mollusca 



63 



Subgenus PROLASMIDONTA Ortmann, 1914. 



Lateral hinge teeth present, but their number re- 

 ^'ersed, two in the right, one in the left valve. Beak 

 sculpture moderately heavy, bars with an angle upon 

 the posterior ridge and a slight sinus in front of it. 

 Inner lamina of inner gills free. Female shell recog- 

 nizable by a slight swelling in the region of the pos- 

 terior ridge. 



Type: Unio Iicterodon Lea, lig. 182. 



Fig. 182 



Subgenus PEGIAS Simpson, 1900. 



Shell small, thickened in front, with a sharp 

 posterior ridge, in front of which is a wide, radial 

 impression, ending in a basal sinus; above this 

 ridge is another, making the shell decidedly biangu- 

 late and truncate behind; beak sculpture consisting 

 of sub-conic corrugations, generally swollen on the 

 posterior ridge ; epidermis decorticated, but showing a few, dark radial 

 rays on the base of the shell ; pseudocardinals rather solid ; laterals wanting. 



Fig. 183 



Type: Margaritana fabula Lea, fig. 183. 



Subgenus RUGIFERA Simpson, 1900. 



Fig. 184 



Shell elongated, rhomboid, inflated, surface brilliantly painted with radi- 

 ations which often break into dappled or splashed pattern of color: pos- 

 terior slope slightly corrugated ; teeth very imperfect ; laterals wanting. 



Type: Alasmodonta inarginata Say, fig. 184. 



