NERITIDA. 295 
Distr.—2 sp. Oligocene and Miocene; Paris and Bordeaux 
basins. D. Neritoides, Grat. (Ixxviii, 59). 
Shell subglobose, thick, umbilicated; spire short; aperture 
entire, semicircular, oblique; columella oblique; callosity den- 
ticulated ; umbilicus covered by the callosity; right lip acute, 
smooth internally. 
This genus presents a very remarkable combination of the 
characters of Natica and Nerita, and appears to establish a pas- 
sage between these two genera, types of distinct families. 
Neritopsis, Grateloup. 
Syn.—Radula, Gray. Peltarion, Desl. Cyclidia, Rolle. Del- 
phinulopsis (in part), Laube. Scaphanidia, Mull. (The last 
three founded on opercula. ) 
Distr.—1 recent and 20 fossil sp. Triassic—; Europe. WN. 
radula, Linn. (xxviii, 60-62). 
Shell subglobular, neritiform, with the spire a little elevated ; 
columellar lip not dentate, largely excavated or sinused in the 
middle. The fossil opercula of this genus were, until recently, 
believed to be the beaks of cephalopods (Peltarion). 
Neritoma, Morris. 
Distr.—Jurassic; Europe. LN. angulata, Sowb. ([xxviii, 63). 
Shell ventricose, thick; apex eroded; aperture with a notch 
in the middle of the outer lip; inner lip excavated in the middle, 
without teeth. Casts of this shell are common, and exhibit the 
condition of the interior characteristic of all the Nerites; it was 
probably fresh water. 
NERIDOMUS, Morris and Lycett. Shell smooth, ovately globose; 
spire small, oblique; the last whorl very large ; aperture ovate 
or semilunar ; outer lip thick, inner lip thick, convex and smooth. 
Great Oolite; England. WN. hemispherica, Romer (1xxviii, 64). 
Neritina, Lam. 
Syn.—Neritella, Humph. Lamprostoma, Swains. 
Distr.—140 sp. Tropical and subtropical; West Indies, 
Europe, India, Philippines, Polynesia, West America. Fossil, 
20 sp. Jurassic, Eocene—. N. communis, Quoy (1xxviil, 65). 
Shell globular, rather thin, aperture-margin thickened ; outer 
lip acute; inner lip straight, denticulated. Operculum shelly 
with a flexible border; exhibiting two processes which von 
Martens calls the “rib” and “peg,” and in which he has found 
the characteristics of several groups of minor value. Animal 
similar to Nerita. 
Neritina can only be distinguished from Nerita by slight dif- 
ferences in the operculum and by the general facies. 
The Neritine are small, smooth globular shells, ornamented 
with a great variety of black or purple bands and spots, covered 
