378 MOLLUSCS, 



which is large 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 aften 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. G. 

 neritcea is a very common Mediterranean shell ; two other species being known, one 

 also Mediterranean, the other from the Black Sea. In the genus Builia 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 Muricidcie 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 



