20 



— without ribs; sh. glassy colorless, white when "dead." 1 2 

 12 whorls well rounded in the spire, which is more or 



less elevated; distinctly, irregularly striated; um- 

 bilicus wide. minuscula, Binn. 



— w^horls scarcely convex in the spire, which is little 



or not elevated, and also rather flattened below; 

 surface scarcely or very finely striated, polished. 



Igeviuscula, Sterki. 



JVofe: — The last five species have not yet been examined for their 

 anatomy, and so their position under llyalinin is still uncertain. — The 

 generic name Zoiiites being occupied for a group of exclusively Euro- 

 pean forms, it should not be used for ours, which range under the genera 

 Hyalinia and Zoiiitoiiks well characterized by anatomic features, 



4. Zonitoides 



1 Sh. with internal lamellae or teeth.* 2 



— Sh. without internal lamelke or teeth. 5 



2 diam. 3.3, alt. 1.5 mill., sh. transparent, horn colored, 



with several internal radial series of small white 

 "teeth;" spire almost flat; whorls 6. 



multidentatus Binn. 



— diam. 5 to 10 mill.; the adult usually with two lam. 3 



3 upper surface with regular ribs, lower smooth; nar- 



rowly perforated; whorls 8; in the palatal wall a 

 strong callus and two toothlike lam. internus. Say. 



— not ribbed 4 



4. spire subconical or low dome-like, inferior side ex- 

 cavated around the narrow or closed umbilicus; 

 whorls 7 to 8, very slowly increasing (the3'Ounger 

 carinated;) surface rather coarsely striated above; 

 color horn, to brownish horn, diam. 8, alt. 5 mill. 



gularis, Say. 



*In old specimens they sometimes are entirely resorbed, as e. g'. in Z. supprexsus^ 

 Say; in the young-, th§ contrary, they niaj' be more numerous than in the adult, St. 



