I062 PHVSUNIO 



Genus PHYSUNIO, Simpson, 1900. 



Physunio Simpson, Syn., 1900, p. 830. 



Shell thin, irregularly obovate, narrowed in front, decidedly 

 produced at post-base, pointed behind and posteriorly winged, 

 with a moderate posterior ridge and often a second or third 

 faint fidge above it; beak sculpture zigzag-radial, somewhat 

 disposed in two sets, the one down the posterior ridge slightly 

 nodulous ; posterior slope having irregular, radial corruga- 

 tions, the rest of the shell smooth ; epidermis often cloth-like, 

 w^ith one or more green rays on the posterior slope ; hinge line 

 curved; a single obliquely granularly striate- pseudocardinal 

 and generally three laterals in the left valve and two pseudo- 

 cardinals and two laterals in the right, all greatly compressed ; 

 beak cavities deep ; muscle scars irregular ; nacre bright, blu- 

 ish, and iridescent. 



Animal unknown. 



Type, Unio graz'idns Lea. 



At first sight the members of this group would seem to be 

 closely related to if not identical in some cases with Hyriopsis, 

 but so far as is known the beak sculpture is very different from 

 that of members of that group, being decidedly zigzag-radial, 

 while that of Hyriopsis is concentric. The inflated forms like 

 graiidus and snperhus appear to be connected with the group 

 Lens through such species as semialatiis and imcropterus. 



Key to species of Physunto. 



Shell much inflated. 



Light greenish or greenish-yellow. gravidas. 



Dark brownish. superbus. 

 Moderately inflated. 



Decidedly inflated. microptenis. 

 Obovate. 



Shell rather large, 80 mm. semialatus. 



Shell rather small, 35 mm. crossei. 



Small, 25 mm., bronzy. cambodiensis. 

 Shell compressed, strongly winged. 



Painted green and yellow. exiynius. 



Uniform yellowish-green. friersoni. 



