NERITIDZ. 297 
on damp foliage above the water. Philippines. N. cornea and 
N. Philippinarum are members of this group—which is too 
close to the typical one. 
SMARAGDIA, Issel. (Gaillardotia, Bourg.) Eyes sessile, not 
stalked. N. viridis, Linn. (Ixxviii, 73). 
NERIPTERON, Lesson. Shell flattened, biauriculated posteriorly ; 
spire posterior, lateral; inner lip septiform, its margin denticu- 
lated. Polynesian. N. vespertina, Recluz (Ixxviii, 74). 
ALINA, Recluz. Shell flattened, dilated posteriorly, the upper 
end of the exterior lip prolonged upon the spire, transversely ; 
inner lip finely denticulated. Scarcely different from Neripteron. 
Polynesia. N. latissima, Brod. (1xxviii, 75). 
Navicetia, Lam. 
Ktym.—Navicella, a small boat. 
Syn.—Catillus, Humph. Cibota, Brown. 
Distr.—33 sp. India, Mauritius, Moluccas, Australia, Pacific. 
N. apiata, Guillou (Ixxviii, 76.) N. Janelli, Recl. (1xxviii, 77). 
Shell oblong, smooth, limpet-like ; with a posterior, submar- 
ginal apex ; aperture as largeas the shell, with a small columellar 
shelf, and elongated lateral muscular scars. Operculum very 
small, shelly, with horny margin, with a lateral apophysis 
(Ixxviii, 78). 
Head large; foot attached on each side to the visceral mass, 
forming a cavity open behind. The operculum is applied to the 
dorsal side of the foot and is concealed in the cavity which it 
forms with the visceral mass. The species, which are exclusively 
East Indian and Polynesian, are usually found on the banks of 
rivers adhering to floating sticks and to the petioles and roots 
of the Nipah palms and other plants that live near the rivers; 
they are also found attached to smooth stones. 
SEPTARIA, Fer, Apex submarginal. N. Hntrecasteauxii, Recluz 
(Ixxviii, 79). 
ELARA, H. and A. Adams. Apex a little elevated above the 
posterior margin, laterally recurved. N. Lapeyrousei, Recl. 
(Ixxviii, 80). 

Dr. Gray has divided the genus from characters derived mostly 
from the opercula, partly from the shells: like the smaller groups 
above noted, these are very unsatisfactory. 
OATILLUS, Humph. (= Navicella, restricted.) Shell elliptical, 
mouth wide ; inner lip flat, shelving, transverse or slightly regu- 
larly arched. Operculum, shelly plate subquadrangular. 
ELANA, Gray. Operculum moderate, thin. 
LAopIA, Gray. Operculum moderate, as long or longer than 
broad, thick; upper lobes subequal, obtuse or acute; the right 
rib indistinct and separated from the margin by a granular space, 
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