37§ 
MOLLUSCS, 
which is laro'e—bifurcated behind. The radula differs from that of the Buccinidce 
in having the central tooth curved and finely serrated. The typical genus Nassa 
comprises an extensive group of small molluscs, which exhibit a considerable 
amount of variation in form and sculpture; and upon these characters many sub¬ 
divisions have been proposed. The shells are mostly solid, ovate or turreted, 
smooth, granulated, or longitudinally ribbed. The aperture has a distinct oblique 
siphonal notch, the columella is more or less coated with callus, and the outer lip is 
thickened and denticulate, or grooved within. About two hundred and forty species 
are recognisable, of which three are met with in Britain. The majority are found 
in tropical seas. They often occur in immense numbers, and burrow in sand 
and mud in search of bivalves. The operculum is often somewhat triangular, with 
fine serrations along the sides. N. reticulata, the largest of the British species, is 
common all round the coast. It is a great nuisance on oyster-beds, and although 
exhibiting a preference for young oysters, also attacks those of more mature 
growth. The egg-capsules are roundish, very compressed, and attached by a short 
stalk to seaweeds. They are arranged close together in compact series, and have a 
small hole at the top, through which the young escape. The subgenus Demoulia 
resembles Nassa as regards the shell, but the animal (of D. retusa at all events) 
has no prolongations at the posterior end of the foot. The operculum is present in 
some species, wanting in others. Four of the seven known species are from West 
and South Africa, and one or two are said to be Japanese. Cyclonassa, another 
subgenus, agrees with the typical Nassa as regards the soft - parts, but is 
characterised by a very aberrant form of shell. This is smooth, flattened, some¬ 
what like a Nerita, and has an oblique distorted look about the aperture. C. 
neritcea is a very common Mediterranean shell; two other species being known, one 
also Mediterranean, the other from the Black Sea. In the genus Bullia the animal 
is very similar to that of Nassa, but the foot is larger, and the eyes are wanting. 
The shells are mostly smooth, and the suture between the whorls is generally filled 
up with a deposit of callus. The south of Africa may be regarded as the 
metropolis of this genus, but a few species also occur on the west and east 
coast, and in Mauritius, Madagascar, and Patagonia. 
The dove-shells, or Columbellidce, are likewise a very numerous family as 
regards species, upwards of three hundred having been described. The animal is 
similar to that of the Buccinidce, but the central tooth of the radula is not armed 
with cusps, and the laterals are of a peculiar type. The shells are all small, some 
quite minute, and offer considerable variation in form and sculpture. Most of the 
species are prettily coloured, and many occur in enormous numbers, and are 
employed in the manufacture of shell-boxes and other ornaments. Columbella 
abounds in the tropics, but many are found in temperate latitudes all over the 
world, and two species belong to the British fauna. All are carnivorous and 
mostly littoral, but some affect depths of five or six hundred fathoms. 
The extensive family of the Maricidce contains some of the handsomest and 
most striking forms of all the Rhachiglossa. The animals have a moderate-sized 
foot, squarish in front and somewhat pointed behind; the tentacles are slender and 
pointed, supporting the eyes on the outer margin. The siphon is long, and the 
retractile proboscis, containing the radula, is well developed. The latter is long and 
