k; 



7 peristome usually with a slight lip at the very mar- 



gin which is slightly everted; whorls 5, well 

 rounded; umbilicus very wide; sh. nearly colorless, 

 translucent; diam. 20, alt. 7 mill. 6. Selenites. 



— peristome-margin quite straight and thin, 8 



8 sh. discoidal, flat above, with very wide umbilicus; 



whorls 4, narrow, convex in the spire with a deep 

 suture, with raised revolving lines; inside with sev- 

 eral oairs of small "teeth;" sh. colorless, or green- 

 ish yellow; diam. 3.5, alt, 1.5 mill. T.Helicodiscus, 



— not so. 9 



9 sh. transparent or translucent, usually shining, 



rarely with ribs. 10 



— sh. rather opaque, surface dull, 12 

 TO diam. 1.5 to 4 mill,; no umbilicus; whorls 4 to 6, very 



narrow; (marginal teeth of radula biscuspid,) 



5. Conulus. 



— larger, or with umbilicus; (marginal teeth of rad- 



ula unicuspid.) 11 



11 genital organs without dart sac and dart, sh. with- 



out lam. or "teeth;" whorls and suture rather 

 flat, or diam. less than 3 mill. 3. Hyalinia. 



— genital organs with dart; sh. with internal lam. or 



teeth, or suture impressed. 4. Zonitoid.es. 



12 diam. 1.5 mill.; spire depressed conic, surface regu- 



larly (verv tiiiel}^) striated; umbilicus wide; whorls 



4; color deep horn. S.Punctum. 



— diam. 2.5; surface w'ith membraneous ribs; S- H3'ali- 



nia. 



— diam, 6 to 25 mill, 13 



13 diam. 6 to 8 mill.; spire depressed conic; surface with 



regular rib-striae; umbilicus very wide; color 

 brownish or reddish horn, 10. Pyramidula. 



— diam. 20 to 25 mill, ; color pale horn, with brown mot- 



tlings or revolving bands. 11. Patula. 



