Synopsis Fresh-Water Mollusca 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 differences more or less noticeable in the shell, often very 

 strongly expressed." (Ortmann.) 



Key to the genera of Lauipsilincc. 

 { Male and female shells alike 2. 



[ ]\rale and female shells different 5- 



r Shell elongate-triangular PtycJiobrancJuis. 



[ Shell rounded-tnangular or oval 3- 



r Shell oval, with a medial row of large tubercles Ohliquarla. 



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



f Epidermis painted with delicate mottlings on a light ground, 



I beak cavities shallow Cyprogenia. 



Epidermis painted with radiating hair-lines, beak cavities 



deep and compressed Droinus. 



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



5. I Female shell slightly sv;ollen just behind the middle of the 



( base Medionidns. 



{ Dorsal margin winged /. 



6. ; 



Dorsal margin not winged 8. 



Pseudocardinals perfect; glochidium celt-shaped, with two 



spines Proptera. 



7- ...... 



Pseudocardinals rudimentary ; glochiduun semicircular, with- 

 out spines Paraptera. 



{Pseudocardinals well developed, complete 9. 

 Pseudocardinals di\'ided into irregular laminre Glehula. 



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 ii. 



f I Tinge heavv and strong; hinge-plate wide and flat Plagiola. 



I TTinge delicate; hinge-plate narrow 4mygdalonaias. 



