328 . THE CHICAGO ACADEMY OF SCIENCES. 
‘Lingual teeth 3-1-3; the rows being more transverse and 
less arcuated than in the Lzttorinid@. Rhachidian tooth broader 
than long,and armed with basal denticles (so-called by Troschel) 
on each side, which may be either on 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 ata 
considerable distance behind the right tentacle. Gills both 
pallial; the right or principal one usually rather short and broad, 
and composed of few laminz, 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 Bythiniine. 
“Shell small, conical; peristome simple or thickened. 
Operculum calcareous or concentric. Fresh water.” (Tryon.)T 
Genus BYTHINIA Gray. 
“Shell: Oval, turbinated, thin, invested with a thin epi- 
dermis, peritreme continuous.” (Tryon.) 
133. Bythinia tentaculata Linné, pl. 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, 6.00; aperture length, 4.50; width, 3.00/mill. (10663.) 
2 11.00; “6.50; Fh ag eae Wh Mom CMT Se (13517.) 
“ 900; "600; “ 450; “ 3850 “  (18517,) 
*Binney’s Land and Fresh Water Shells N. A., part III, p. 65. 
+S. and S. Conch., Vol. II, p. 260. 
