Synopsis Frf.sh-Watkr Mollusca 

 Genus TRITOGONIA Agassiz, 1852. 



45 



Shell solid, elongate, rhomboid, having a strong, irregular posterior 

 ridge, obliquely truncated behind in the male, in the female this region is 

 somewhat compressed and expanded into a broad wing; base curved; whole 

 surface, exxept the rounded wing of the females, covered with pustules ; 



Fig. 147 



beaks rather low, incurved and turned forward over the well developed 

 lunule; beak sculptiu'e strong, consisting of irregular, subparallel ridges 

 which are curved upwards behind and fine radiating ridges in front of and 

 behind them ; epidermis dark olive ; hinge plate rather narrow ; pseudo- 



Fig. 147 



cardinals strong, ragged; laterals long and straight, near to the pseudo- 

 cardinals; cavity of beaks rather deep and compressed; female shell more 

 compressed than that of the male. Marsupium occupying all four gills. 



Type: Unio inherculains Bar., fig. 147. 



