ZONITID^. 21 



are depressed globose, pellucid or corneous, smooth and shining 

 both on the upper and under surface. Two long tongue-shaped 

 shell-lobes ; the left cervical lobe divided into two. N. specta- 

 bilis, Pfr. 



EURYPUS, Semper, 18Y0. Foot with the back broad, not 

 carinated. N. casca, Gould. Fiji Isles. 



ROTULARiA, Mirch, 1872. Uncharacterized. N. Beinhardi, 

 Morch. Nicobar Isles. 



GERONTiA, Hutton, 1883. Shell depressed, umbilicated, of about 

 five gradually increasing M^horls, aperture oblique, margin not 

 reflected, thin. Animal heliciform; mantle rather posterior, 

 included ; tail acute, with a mucous pore, but no papilla. Jaw 

 smooth, striated. H. panther ina, Hutton. New Zealand. 

 Differs from Patula in having a mucous pore. 



MEDYLA, Gray, 1855. (Otesia, H. and A. Adams, 1855.) Shell 

 imperforate or scarcely rimate, depressed, thin ; whorls few, 

 rapidl}^ increasing, the last rounded or carinate ; aperture large, 

 angulately lunar ; lip simple, acute. N. fecta, Sonl. 



AMPHiDOXA, Albers, 1850. Shell perforated, depressed, thin, 

 pellucid ; whorls convex, rapidly increasing ; aperture very 

 oblique, large, oval; peristome simple, its extremities connected 

 by a very thin callus. N. marmoreUa^Ffr. 2sp. Juan Fernandez. 



MICROCYSTIS, Beck, 1837. (Helicopsis, Beck, 1887. ? Platy- 

 closter, Hasselt.) Shell small, subperforated, glabrous ; aperture 

 large, subvertical. N. Adamsi, Pfr. (xciii, 83). Pitcairn's Isl. 



MICROCYSTINA, Morch. Shell polished, with a small notch at 

 the pillar-lip. N. .Rinki^ Morch. Nicobar Is. 



SESSARA, Albers, 1860. Shell imperforate, depressl}^ oi-bicular, 

 costulate-striate above, angulate on the periphery ; base smooth, 

 excavated ; aperture depressed, wide, toothed. N. infrendens^ 

 Gould. Distinguished from other Naninae by the thickened colu- 

 mellar lip and toothed aperture ; mantle-lobes small. Jaw smooth, 

 finely radiate-striate on the inner side, with an obtuse middle 

 projection. 



THALASSIA, Albers, I860. Shell imperforate or scarcely per- 

 forate, conic-orbicular, thin, pellucid ; whorls five or six, slowly 

 increasing, the last angulate or carinate, umbilical region im- 

 pressed ; peristome simple, acute ; columellar margin slightly 

 reflexed. N. subj-ugata, Pfr. 



SOPHINA, Benson, 1850. Foot long, obliquely truncate at its 

 posterior end, with a lai'ge gland and distinct horn-like append- 

 age ; mantle-lobes as large as in Helicarion. Shell with a callous 

 columella, angulated at the basal margin, and with a more or less 

 acute umbilical carina. N. Calias, Benson. 



HEMiPLECTA, Albers, 1850. Shell granulose or striated above, 

 polished below ; last whorl more or less angular or carinated 



