Bryant Walker 



Key to the subgenera of Lynuicva. 



{Spire elevated 2. 

 Spire short 6. 



(Body-whorl greatly inllated Lymncca s. s. 

 Body-whorl slightly inflated 3. 



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



3. i tinuous Acclla. 



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



[ lip not continuous 4- 



f Columella smooth, reflected over the umltilicus Galha. 



[ Columella twisted or plicate 5- 



f Surface with impressed, spiral lines Stagnicola. 



[ Surface longitudinally costate Polyrhyiis. 



{ Body-whorl large, not inflated, elongate Pscndosnccinca. 



[ Body-whorl large, inflated 7- 



{ Shell large, solid, bulimiform ; lip not expanded BnUnmcva. 



7. \ 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;EA 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- 

 Fig. I tral and bicuspid lateral teeth, marginals serrate. 



