Synopsis Fre;sh-Wate:r Moli^usca 65 



without spine, rarely celt-shaped and with two spines ; shell heavy or lighter, 

 rounded, or oval to elongate; color of the epidermis rarely dull, mostly 

 •bright, with color markings; sculpture of the beak generally. double-looped, 

 but often obsolete, more rarely concentric; hinge generally complete, with 

 well developed teeth, which only in rare cases show a tendency to become re- 

 duced; sexual dififerences more or less noticeable in the shell, often vei-y 

 strongly expressed." (Ortmann.) 



Key to the genera of LanipsilincE. 

 { Male and female shells alike • 2. 



[ Male and female shells different 5- 



r Shell elongate-triangular _. Ptychobranchus. 



[ Shell rounded-triangular or oval 3- 



f Shell oval, with a medial row of large tubercles Obliquaria. 



3-i 



[ Shell rounded-triangular, nodulously wrinkled or lachrymose. ... 4. 



Epidermis painted with delicate mottlings on a light ground, 



beak cavities shallow • • Cy progenia. 



Epidermis painted with radiating hair-lines, beak cavities 



deep and compressed Droiiuts. 



r Female shell more or less expanded in the post-basal region 6. 



5. \ Female shell slightly SAVollen just behind the middle of the 



[ base Medionidns. 



{ Dorsal margin winged 



6. . 



Dorsal margin not winged 



Pseudocardinals perfect; glochidium celt-shaped, with two 



spines Proptera. 



Pseudocardinals rudimentary; glochidium semicircular, with- 

 out spines Paraptera. 



Pseudocardinals well developed, complete 9. 



[ Pseudocardinals divided into irregular laminae Glehida. 



f Shell with a distinct posterior ridge, dorsal-slope smooth 10. 



9. \ Shell usually without a distinct posterior ridge, or when dis- 



[ tinct, dorsal-slope radiately sculptured 11. 



f Hinge heaw and strong; hinge-plate wide and flat Plagiola. 



1 Hinge delicate ; hinge-plate narrow Amygdalonaias. 



