42 Bryant Walker 



Key to the subfamilies of Unionidce. 





2. 



Water-tubes simple in the gravid female v 



Water-tubes in the gravid female divided into three tubes, 

 [ of which only the centre one is used as an ovisac Anodontince. 



Male and female shells usually alike ; edge of the gravid 



marsupium always sharp and not distending UnionincE. 



Male and female shells usually different ; edge of the gravid 

 marsupium distending and bulging out beyond the original 

 edge of the gill Lanipsilincc. 



Subfamily UNIONIN^ (Swainson, 1840) Ortmann, 1910. 



"Inner lamina of the inner gills generally free from the abdominal sac 

 (sometimes, in extralimital forms, connected) ; supra-anal opening some- 

 times not separated from the anal, normally present, the closed part rather 

 short ; branchial opening well-defined ; no papillae nor flaps on the edge of 

 mantle in front; marsupium formed by all four gills or by the outer gills 

 only; edge of marsupium always sharp and not distending; water-tubes not 

 divided in the gravid female ; glochidium semielliptic or semicircular, with- 

 out spines; shell generally heavy and solid, rounded to elongated, mostly 

 with dull-colored epidermis; sculpture of the beak generally rather indis- 

 tinct, concentric or pustulous or with indications of double loops or zig- 

 zag bars ; hinge always complete, with rather strong teeth ; generally no 

 difference of sex shown in the shell." (Ortmann.) 



Key to the genera of Unionince. 



r All four gills serving as marsupia 2. 



[ Outer gills only serving as marsupia 6. 



f Male and female shells alike 3. 



[ Male and female shells different Tritogonia. 



f Hinge with perfect pseudocardinals and laterals 4. 



3- ^ . 



[ Hinge teeth rudimentary or wanting Gonidea. 



f Surface plicate e^^ 



4. \ Surface pustulose Quadnila. 



[ Surface smooth ,Fusconaia. 



5-i 



Beaks sculptured with coarse, concentric or somewhat dou- 

 ble-looped ridges, which do not extend over the smia.ce. Amblcina. 



Beaks sculptured with strong, zig-zag ridges extending over 



the upper surface ." Megalouaias. 



