I. 



2. 



5- 



6. 



Bryant WaIvKEr 



Key to the subgenera of Lymncea. 

 Spire elevated ; 2. 



Spire short 6. 



Body- whorl greatly inflated Lymncea s. s. 



Body-whorl slightly inflated 3. 



Shell very slender ; spire longer than the aperture ; lip con- 

 tinuous Acclla. 



Shell more or less inflated ; spire shorter than the aperture ; 



lip not continuous , 4. 



Columella smooth, reflected over the umbilicus :Galba. 



Columella twisted or plicate 5- 



Surface with impressed, spiral lines Stagnicola. 



Surface longitudinally costate Polyrhytis. 



Body-whorl large, not inflated, elongate Pseudosuccinea. 



Body-whorl large, inflated 7- 



Shell large, solid, bulimiform; lip not expanded. . . Bulmincea. 



Shell moderate, spire very short, usually thin, lip more or 



less expanded 8. 



Shell thin, lip widely expanded, surface polished ; spire 

 acute, whorls rounded Radix. 



Shell thicker; lip occasionally expanded; lines of growth 



distinct; spire broad, whorls shouldered Stagnicola (pars). 



Subgenus LYMN^A s. s. 



Shell large, thin, with an acute, slender spire and 

 expanded body- whorl; axis gyrate, forming a (usually) 

 pervious spiral coil without a true umbilicus ; the callus 

 on the body-whorl closely appressed; the outer lip flar- 

 ing more or less, simple, sharp, normally without any 

 thickening. Penis-sac very large; penis very short 

 (about one-quarter the length of the penis-sac) ; penis 

 retractors normally two, very large ; anterior termination 

 of the prostate bulb-shaped. Radula with unicuspid cen- 

 tral and bicuspid lateral teeth, marginals serrate. 



