374 
MOLLUSCS, 
the shell; and when disturbed it not unfrequently casts off the hinder part. 
About ten species are recognisable. They occur in the Red Sea, many parts of 
the Indian Ocean, Philippine Islands, South Sea Islands, Panama, and on the 
west coast of Africa and at Ascension Island. The members of the family 
Marginellidce are mostly small, some very minute, but many of them have 
very beautifully coloured and highly polished shells. Nearly all are tropical, and 
many of the finest and most valued are inhabitants of the West and South 
African coasts. They are mostly ovoid, or subconoidal in form, with rather con¬ 
tracted apertures, slightly notched in front; the outer lip is involute and thickened, 
and the columella has a few oblique plaits upon the lower or anterior portion. 
There is no operculum ; and, as in the majority of the volutes, the radula has only a 
central row of teeth. In Pseudomarginella, from Goree, on the west coast of 
Africa, the shell is identical in every respect with Marginella glabella of the 
same locality, but the mollusc and its operculum are said to belong to the Buccinidce. 
Nearly all the species of the family Volutidce have large showy shells, and 
some of them, on account of their extreme beauty and rarity, realise very high 
prices. As in the Marginellidoe, the columella exhibits a number of oblique folds, 
but the aperture is rather more deeply notched in front for the passage of the 
siphon. The form of the shell is variable; in some the spire being very short, 
and scarcely rising above the last or body-whorl; while in others ( Zidona ) it is 
drawn out into a conical spire. The apex is sometimes (as in Yetus) enormous, 
and all intermediate sizes occur until we come to Volutilithes, in which it is quite 
small. This latter genus—a very common Eocene fossil of the London and Paris 
basins—has very feeble columellar plaits, and is now represented by a single species 
obtained in one hundred to one hundred and fifty fathoms off the Cape of Good Hope. 
The animals of the volutes are large, sometimes incapable of withdrawing entirely 
within the shell, and mostly without an operculum. The radula usually has only a 
single row of teeth, but, in a few instances, a lateral on each side is present. The 
Yetus shells are large, thin, with enormous apertures, having three or four strong, 
oblique plaits on the columella. They are found on the west coast of Africa, in the 
Indian and Pacific Oceans, and also off the Philippine Islands. Y. proboscidalis is 
viviparous, and produces four or five young at a time, about an inch long. The 
flesh of this enormous animal is said to be eaten, after being dried in the sun, by the 
natives of Senegal. As an example of the genus Voluta, we may mention the hand¬ 
some West Indian V. musica, popularly known as the music-shell, from the colour- 
markings, which resemble the lines and notes of music. It is one of the few forms 
provided with a small horny operculum, and on this account has been placed in a 
distinct genus ( Volutolyria ) by some writers. Like the rest of the true volutes, 
it is oviparous. The allied genus Volutomitra, as the name implies, has affinities 
both with Voluta and Mitra ; the shell and animal being for the most part 
mitroid, but the tongue resembling that of the volutes. It may therefore be 
regarded as a link between the two families. Three or four species are known, 
one from the shores of Greenland, and two or three from Tasmania and Kerguelen 
Island. The largest member of the Volutidai (Cymbium broderipi), which is 
found at the Philippine Islands, sometimes attains a length of 14 inches and 30 
in circumference. Rather more than a hundred species of this family are known. 
