68 



Bryant Walker 



Genus DROMUS Simpson, 1900. 



Shell solid, rounded triangular; beaks well forward, rather high; beak 

 sculpture consisting of fine ridges running parallel with the growth lines, 

 the furrows between the ridges interrupted at the posterior ridge ; posterior 

 ridge distinct; a series of humps runs from the beaks down to the central 

 part of the base of the shell, which is otherwise sculptured by irregular, 

 concentric ridges ; epidermis beautifully painted by undulated, radiating, 



^ sa 



,an 



^br 



mp 



Fig. 191 Fig. 192 



broken hair-lines or fine maculations ; hinge plate wide and fiat ; pseudo- 

 cardinals triangular, small and low, ragged ; laterals low, short, club-shaped ; 

 cavity of the beaks deep and compressed ; front part of the shell very thick, 

 suddenly becoming thinner at the row of humps. Marsupium occupying the 

 base of nearly the whole outer gills in numerous narrow ovisacs, which 

 extend beyond the original edge of the gill. 



Type: Unio dramas Lea, fig. 191. Animal, frontispiece, fig. 192. 

 Genus CYPROGENIA Agassiz, 1852. 



Shell solid, infiated, rounded, triangular, sometimes slightly retuse, gen- 

 erally a little biangular behind ; posterior ridge usually well developed ; um- 

 bonal region fiattened parallel with the axis of the shell, sometimes com- 



-.sa 



Fig. 193 



