ZONITIDA. 27 
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, 1870. Foot with the back broad, not 
carinated. N. casca, Gould. Fiji Isles. 
ROTULARIA, Mirch, 1872. Uncharacterized. N. Reinhardi, 
Mirch. Nicobar Isles. 
GERONTIA, Hutton, 1883. Shell depressed, umbilicated, of about 
five gradually increasing whorls, 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. pantherina, 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, 
rapidly increasing, the last rounded or carinate ; aperture large, 
angulately lunar; lip simple, acute. WN. tecta, Soul. 
AMPHIDOXA, Albers, 1850. Shell perforated, depressed, thin, 
pellucid ; ‘whorls convex, rapidly increasing; aperture very 
oblique, large, oval; peristome simple, its extremities connected 
byavery thincallus. N.marmorella, Pfr. 2sp. Juan Fernandez. 
Microcystis, Beck, 1837.. (Helicopsis, Beck, 1837. ? Platy- 
closter, Hasselt.) Shell small, subperforated, glabrous; aperture 
large, subvertical. N. Adamsi, Pfr. (xciii, 83). Pitcairn’s Isl. 
MrtcRocysTINA, Mirch. Shell polished, with a small notch at 
the pillar-lip. N. Rinki, Morch. Nicobar Is. 
SESSARA, Albers, 1860, Shell imperforate, depressly orbicular, 
costulate-striate above, angulate on the periphery ; base smooth, 
excavated ; aperture depressed, wide, toothed. WN. infrendens, 
Gould. Distinguished from other Nanine 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, 1860. 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. subrugata, Pfr. 
SOPHINA, Benson, 1859. Foot long, obliquely truncate at its 
posterior end, with a large 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. 
HEMIPLECrA, Albers, 1850. Shell granulose or striated above, 
polished below; last whorl more or less angular or carinated 
