NERITID^. 29t 



on damp foliage above the water. Philippines. N. cornea and 

 N. Fhilippinai'um are members of this group — which is too 

 close to the typical one. 



SMARAGDiA, Isscl. f Graillardotia, Bourg.) Eyes sessile, not 

 stalked. . N. viridis, Linn. (Ixxviii, 13). 



NERiPTERON, Lcsson. Shell flattened, biauriculated posteriorly ; 

 spire posterior, lateral; inner lip septiform, its margin denticu- 

 lated. Polynesian. N. vespertina, Recluz (Ixxviii, 14). 



ALiNA, Recluz. Shell flattened, dilated posteriorly, the upper 

 end of the exterior lip prolonged upon the spire, transversel}^ ; 

 inner lip finely denticulated. Scarcely different from Neripteron. 

 Polynesia. N. latissima, Brod. (Ixxviii, 75). 



Navicella, Lam. 



JEtym. — JVavicella, a small boat. 



Syn. — Catillus, Humph. Cibota, Brown. 



Distr. — 33 sp. India, Mauritius, Moluccas, Australia, Pacific, 

 N. ajjiata, Guillou (Ixxviii, 16.) N. Janelli^ Reel. (Ixxviii, 77). 



Shell oblong, smooth, limpet-like ; with a posterior, submar- 

 ginal apex ; aperture as large as 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, Per. Apex submarginal. N. E ntrecasteaiixii,'Reclnz 

 (Ixxviii, 79). 



ELARA, H. and A. Adams. Apex a little elevated above the 

 posterior margin, laterallj^ recurved. N. Lapeyrousei, Reel. 

 (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. 



CATILLUS, 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. 



LAODTA, 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, 

 20 



