226 ON THE NAIADES, 



Bead before the .American Philosophical Society, Jipril I8th, 1834. 



Lymn^a acuta. Plate XIX. fig. 81. 



Testa elongato-turrild, tenui, Imvi, fusco-nigricante ; spird attenuata; aiifrac- 

 tibus senis ; aperturd subovatd. 



Shell elevated, turrited, thin, smooth, dark brown; spire attenuate; whorls six; 

 aperture subovate. 



Hab. pond four miles north of Philadelphia. 

 Diam. -3, Length -7 of an inch. 



Remarks. — This delicate species, although attenuate, is not so much 

 so as the exilis herein described. Its whorls are more convex and the 

 body whorl larger, the aperture being about one half the length of the 

 shell. Several specimens were found by me some years since, in a 

 very small pond near to the Falls of Schuylkill. Since then this pond 

 has occasionally dried up, and I have not been able to find others. 

 Although there are other ponds near to this, which other species in- 

 habit, I have never been able to discover the acuta in any other spot. 



Lymn^a exilis. Plate XIX. fig. 82. 



Testd atteniiatd, tenuissimd, longitudi7ialiter striatd; anfractibus septenis, 

 2}lano-convexis ; columelld reflexd; aperturd ovato-oblongu. 



Shell attenuated, very thin, longitudinally striate ; whorls seven, plano-convex ; 

 columella reflected ; aperture ovato-oblong. 



Hab. Ohio, T. G. Lea. 



My Cabinet. 

 Diam. '4, Length 1'5 inches. 



