82 SYSTEMATIC ARRANGEMENT 



B. Licinina. Operculum nearly orbicular, composed of a few gra- 

 dually-increasing whorls ; nucleus somewhat excentrical. 



a. Operculum thick, testaceous. 



16. Jamaicia. 



Operculum shelly, externally convex, composed of a small number 

 of obliquely-striate, rather coarse, sublamellar whorls. Shell urn- 

 bilicate, globose-conical ; aperture circular. Peristome simple or 

 double, straight or reflected. 



1. J. anomala. 



17. LlCINA. 



Operculum ? Shell conical ; last whorl usually produced 



out of the spiral line, straight ; mouth circular. Peristome some- 

 what reflexed, expanded. 



1. L. labia. 



18. Choanopoma. 



Operculum calcareous, nearly circular, with gradually-enlarging 

 whorls, terminating externally in more or less prominent, thin 

 lamellae, with a subexcentrical nucleus. Shell globose-turbinate or 

 turrited, often truncate ; aperture rather oval or roundish. Peristome 

 usually double, with the outer edge angularly expanded. 



1. C. pulchra. 



b. Operculum thin, cartilaginous. 



19. Adamsiella. 



Operculum orbicular, thin, rather cartilaginous ; whorls few, en- 

 larging gradually, with the outer edge rather detached ; nucleus 

 subcentral. Shell Pupa-shaped or oblong-turrited ; aperture small, 

 rather circular. Peristome for the most part double, more or less 

 expanded or reflexed. 



1 . A. mirabilis. 



C. Cyclostomina. Operculum ovate, composed of few whorls, more 

 or less rapidly enlarging, with the nucleus excentrical. 



a. Operculum thick, with an external shelly coat. 



20. Lithidion. 



Operculum subcircular, shelly ; whorls rather rapidly enlarged, 

 with h strong, convex, subcentral keel and simple edges. Shell de- 

 pressed, broadly umbilicated, open ; aperture rather circular. Peri- 

 stome simple, often thickened. 



1. L. sulcatum. 



