Synopsis Fresh-Water Moleusca 



49 



iile; beak sculpture consisting of numerous, fine, irregular, broken, some- 

 what concentric corrugations; posterior three-fifths of ihe shell tuberculate ; 

 epidermis brown ; nacre purple. 



Only the outer gills serving as niarsupiuni. 



o = mp 



Fig. 155 

 Type: Ohliqitaria (Rotnndaria) iubcrcnlata Raf., fig. 154. Animal, fig. 155. 



Genus PLETHOBASUS Simpson, 1900. 



Shell large, irregularly oval, inflated, solid, somewhat suddenly swollen 

 at the posterior base; posterior ridge low and rounded; beaks rather high, 

 near the anterior end, having a few strong ridges, which are curved up- 



V\g. 156 



wards behind ; a row of low, irregular tubercles extends from near the 

 beaks to post-basal part of the valves; epidermis tawny yellow to dark 

 brown ; hinge plate solid, not flattened ; pseudo-cardinals triangular, rough ; 



