Synopsis Fri;sh-Wate:r Moi^lusca 

 Subgenus TRUNCILLA s. s. 



8i 



Fig. 217 



mp PP 



Fig. 218 



Shell covered with broken rays, somewhat triangular and without a wide, 

 radiate, posterior furrow. 



Type: T. triquefer Raf., fig. 217. Animal, fig. 218. 



Subgenus SCALENARIA (Rafinesque, 1820) Agassiz. 



Fig. 219 



Male shell having a wide, radiating, shallow depression in front of the 

 ]iosterior ridge ; that of the female having a small, rounded, well-defined, 

 radial post-basal swelling. 



'J'ype : Unio siilcatiis Lea, fig. 219. 



