"_Mitra_ is a large genus, and it is believed that there are three times as many species yet undescribed. The mitres are natives of warm climates, and few are common. The pillar-lip of _Mitra_ is parallel, with transverse folds; the base has a slope, but no canal; the margin of the columella is thin and rolled back. _M. episcopalis_, the bishop, is white with red spots; the columella-folds are four. (Plate 9.) _M. papalis_, the pope's-mitre, has five; the upper whorls are broken into a kind of crown. "In _Cymba_, the gondola, the spire ends in a tubercle, and scarcely appears; the aperture is wide: they are very pretty shells. "_Melo_, the melon, from the Indian Ocean, is a very fine genus; here the spire is evident. "_Voluta musica_ will serve as an example of the genus. The animal is carnivorous. "_Marginella_ is an oblong, smooth, and polished shell; its peculiar character is the thickened outer lip; it is a neat, small species, prettily coloured. "_Volvaria_ is a cylindrical shell, convolute, the spire nearly hidden; the aperture straight, as long as the shell. There is a fossil species found in London clay. _V. monilis_ is sometimes strung for necklaces. It comes from Senegal. [Sidenote: OVULA.] "The last family of the order _Trachelipoda_ is _Convoluta_, which contains many very fine genera. "They are the following: _Ovula_ _Bulla_. _Cypræa_ The same. _Terebellum_ _Bulla_. _Ancillaria._ _Oliva_ _Voluta_. _Conus_ The same. "The general characters of this family are the following: "Shell without a canal, the base of the aperture sloping, or effuse, the spire compressed, the last volution almost covering the rest. "_Ovula_, you will recollect, was formerly confounded with the _Bulla_ genus: the form is egg-shaped, the outer lip toothed in one division, smooth in the other; the shells are white and polished, particularly _O. oviformis_, the poached-egg, from the Moluccas. "_O. volva_, the weaver's-shuttle, is a rare and highly-valued species. It is nearly globular in the middle, and is terminated at each extremity by a long beak: it comes from the West Indies. _O. gibbosa_ is a common species; the shape is oblong, with a ridge in the centre. [Sidenote: CYPRÆA. TRIVIA.] "You can be at no loss on seeing the shells of _Cypræa_, a large and beautiful genus, which remained unchanged for a long time. Lately, we find a few of the small species are become a new genus, _Trivia_. "The character of the _Cypræa_ is a longitudinal aperture, toothed, in the adult state, on each side. The spire is scarcely to be seen. "While the shells are young they have the appearance of a _Voluta_ or a cone; the aperture spreads more, and is without teeth. "The individuals of each species pass through three different states: