FAMILY 3. NERITACEA. 141 
however, are found to differ essentially from the Nerit@, especially in the 
formation of the shell at the columella, there being a singular kind of gap 
in the middle of it, which looks exactly as if a square piece had been 
chipped out with a chisel, or as if the pillar of the shell had been partially 
eaten away by a crab. 
The shell of Neritopsis may be described as being of an obovate form, 
consisting of three or four whorls, increasing rapidly in size, with a short 
spire, which is sharp and somewhat raised at the apex; the aperture is 
transverse, nearly semilunar, and the margins are disjoined, the lip being 
thickened, and deeply striated to within a given distance on the inside ; 
the columella is solid, and widely notched out near the middle. The 
operculum is thin, horny, and simple. 
Examples. 
Pl CCTs Biz: 
Neriropsis CANCELLATA, Sowerby, Genera of Shells, No. 42. 
Nerita radula, Linneus. Chemnitz, Conch., vol. v. pl. 190. f. 1946 and 
1947. 
Platystoma granulatum, Klein. 
Pl. CCIII. Fig. 2. (fossil.) 
NERITOPSIS GRANULATA, Sowerby, Genera of Shells, No. 42. 
Pl. CCIII. Fig. 3. (fossil.) 
NERITOPSIS GRANOSA, Sowerby, Genera of Shells, No. 42. 
and he proposes the title of Vanzkoro, after its locality ; but this word must be abandoned,—it 
is both ungrammatical, and opposed to all rules of nomenclature. Gray, with his accustomed 
alacrity, has not only accepted the genus Vanikoro, but created a special family for its recep- 
tion, Vanicoroide ; we cannot, however, agree with him in placing it next in order to the 
Capulacea, for it is evident that there is the same important difference between Vanikoro (Ve- 
lutina cancellata) and Pileopsis, as we have already noted to exist between Navicella and 
Crepidula; in one the shell exhibits a perfect regularity of growth, is free and operculated ; 
in the other it always remains adherent, and becomes shapen to the irregularities of its place 
of attachment. 
