OF MOLLUSCA. 81 



c. Pupinina. Operculum horny, thin, many-whorled, without any 

 external calcareous layer. Shell oblong, elongate ; last whorl 

 with a fold or spiral ridge on the inner side in front of the 

 axis, sometimes forming a groove in the inner lip. 



10. Megalomastoma. 



Operculum orbicular, thin, horny, many-whorled, rather flat, 

 Shell narrowly or scarcely perforate, oblong, turrited or Pupa- 

 shaped ; aperture rather circular, sometimes furnished with a slight 

 lateral channel. Peristome double or simple, rather thickened, 

 rarely straight. 



1. M. brunnea, t. 311. f. 15. 



11. Cataulus. 



Operculum orbicular, flat, horny, many-whorled, separable into 

 many plates, forming a continuous spiral lamina like a corkscrew. 

 Shell perforate, Pupa-shaped, not callous, furnished with a filiform 

 basal keel ; aperture entire, prolonged at its base by a rather cir- 

 cular channel. Peristome continuous, dilated at its lower extremity 

 into the keel of the last whorl. 

 1. C. tortuosus. 



12. PUPINELLA. 



Operculum horny, many-whorled. Shell oval, covered with a thin 

 horny periostraca ; aperture circular. Peristome reflexed, thickened, 

 with a groove on the inner side of front near the axis. 



1. P. pupiformis. 



13. Pupina. 



Operculum thin, membranous, narrow-whorled, rather flat. Shell 

 Pupa- shaped, for the most part covered by a smooth callus. Peri- 

 stome simple, thickened or reflected ; columellar margin divided in 

 the middle by a transverse channel ; right margin forming a second 

 channel at its insertion. 



1. P. humilis. 



14. Registoma. 



Operculum orbicular, thin, horny, many-whorled. Shell ovate, 

 polished, callous ; aperture circular, rather entire. Peristome re- 

 flected ; inner lip thin, simple ; columellar margin slightly curved 

 and channeled in the middle. 



1. R. grandis. 



15. Callia. 



Operculum thin, membranous, narrow-whorled. Shell pupiform, 

 covered with a smooth shining callus. Peristome subcontinuous, 

 straight, scarcely thickened ; columellar margin entire, above ap- 

 pressed-reflexed, altogether closing the perforation, which is conspi- 

 cuous in young shells. 



1. C. lubrica. 



