328 THE CHICAGO ACADEMY OF SCIENCES. 



"Lingual teeth 3-1-3; the rows being more transverse and 

 less arcuated than in the Litlorinidce. Rhachidian tooth broader 

 than long, and armed with basal denticles(so-called by Troschel) 

 on each side, which may be either qn the basal margin, or on 

 the anterior surface of the tooth above the base; cusp recurved 

 and denticulated. Intermediate tooth more or less hatchet- 

 shaped, having a handle-like process (peduncle) projecting out- 

 wardly from the base of the broad body which is denticulated 

 at the upper margin. Lateral teeth generally slender and 

 armed with numerous minute denticles at their superior mar- 

 gins. Verge (male organ) exserted, situated on the back at a 

 considerable distance behind the right tentacle. Gills both 

 pallial; the right or principal one usuallyrather short and broad, 

 and composed of few laminae, which are much broader than 

 high. Foot oblong, truncate before, rounded or pointed be- 

 hind. Operculigerous lobe well developed." (Stimpson.)* 

 "Inhabits fresh water in all parts of the world." (Tryon.) 



Subfamily Bythiniinas. 



"Shell small, conical; peristome simple or thickened. 

 Operculum calcareous or concentric. Fresh water." (Tryon.)f 



GENUS BYTHINIA Gray. 



"Shell: Oval, turbinated, thin, invested with a thin epi- 

 dermis, peritreme continuous " (Tryon.) 



133- Bythinia tentaculata Linne, pi. xxx, fig. 34. 



Turbo tentaculata LINNE, Syst. Nat. Ed. XII, p. 1249. 



Shell: Globose, rather thick, transparent to opaque; color 

 ranging from yellowish to greenish, sometimes brownish; sur- 

 face shining, smooth, lines of growth very fine; sutures very 

 deeply impressed; whorls five, convex, the last rapidly en- 

 larging and equaling all the others combined; spire elevated, 

 broadly conic; apex small, round, reddish-brown; aperture 

 broadly rounded-ovate, narrowed above; peristome thin, 

 rounded, simple, continuous, thickened a little on the inside, 

 bordered all around with yellowish; base of shell rounded, 

 imperforate. 



Length, 9.50; width, 6.00j aperture length, 4.50; width, S.00jnill. (10663.) 

 11.00; " 6.50; " " 4.50; " 3.50" " (13517.) 



9.00; " 6.00; " " 4.50; " 3.50 " (13517.) 



*Binney's Land and Fresh Water Shells N. A., part III, p. 65. 

 t S. and S. Conch.. Vol. II, p. 260. 



