65 



Greatest length of the body whirl, one-fourth of an inch Breadtyi 

 from tip of the hibruni, one half of an inch ; at right angles to the 

 last, two-fifths of an inch. 



This shell abounds in some of the small streams, which discharge 

 into Cayuga lake, where it was collected by Mr. Jessup, who pre- 

 sented specimens to the Academy, and to me. It is readily dis- 

 tinguished from our other species, by the sudden dilatation of the 

 outer whirl, near the aperture in the adult shell, forming a large 

 oval chamber. The summit of the outer whirl, behind the dilated 

 portion, is not, or hardly elevated above the summits of the other 

 volutions. 



Lymneus elongatus. — Shell horn color, tinged with reddish- 

 brown; spire elongated, tapering, acute; whirls six or seven, 

 slightly convex, wrinkled across ; body whirl, measured at the 

 back, more than half the total length ; suture moderately indented ; 

 aperture less than half the length of the shell ; labium with calca- 

 reous deposit. 



Length, one inch and three-tenths. 



Inhabits in considerable numbers, the ponds and tranquil watert< 

 of the Upper Missouri. It is very distinct from L. catascopiunij 

 by the much greater proportional length of the spire. 



Lymneus columellus. — (Jour. Acad. Nat. Sciences, vol. i. 

 p. 14.) Var. a. Small, black — from Cold water creek of the Mis- 

 souri. This is most probably a distinct species ; we obtained but a 

 single specimen of it. 



Lymneus reflexus. — Shell fragile, veiy much elongated, nar- 

 row, honey-yellow, tinctured with brownish, translucent, slightly 

 reflected from the middle ; volutions six, oblique, wrinkled trans- 

 versely ; spire more than one and an half times the length of the 

 aperture, acute, two or three terminal whirls vitreous ; body whirl 

 very little dilated ; aperture rather narrow ; labrum with a pah- 

 margin, and dusky red or blackish sub-margin. 



Inhabits Lakes Erie and Superior. Total length, 13-10 — of the 

 aperture 11-20 of an inch. 



This shell is remarkable for its narrow and elongated form, and 

 for the consequent, very oblique revolution of its whirls. When 

 viewed in profile, it has a slightly reflected appearance. It wat; 

 kindly sent to me for examination by my friends Messrs. S. B. 



