It was deemed advisable, as this is intended for an easy introduction to the science, to omit many divisions and subdivisions, which would only serve to perplex and render the attainment more difficult. As the Naiades, or shells of this country, are given in several valuable scientific works lately published, we have only slightly touched them in the place they are intended to occupy. We cannot expect that the work now presented to the public is free from imperfections; but we ask for their lenity and kind forbearance to excuse whatever defects there may be in our humble attempts to advance the cause of science. Conchology, like other departments of natural history, is progressing; and that which is given to-day is almost always susceptible of being modified to-morrow; should this work be well received, it is our intention to give, as soon as practicable, an enlarged work, containing even the minute microscopic shells and the fossils, with plates containing types of as many species of the genera as can possibly be obtained. The plates were drawn and coloured with great care and accuracy from the natural shells in our own cabinet, under the superintendence of Mr. James Ackerman, artist. T. W. ARRANGEMENT. CLASS I. ANNELIDES. FOUR FAMILIES. Fam. 1. _Dorsaliæ._ Two genera. 1. Arenicola. Species 1 2. Siliquaria. “ 4 2. _Maldaniæ._ Two genera. 1. Clymene. Species 1 2. Dentalium. “ 12 3. _Amphitritæa._ Four genera. 1. Pectinaria. Species 2 2. Sabellaria. “ 2 3. Terebella. “ 3 4. Amphitrite. “ 6 4. _Serpulacea._ Five genera. 1. Spirorbis. Species 5 2. Serpula. “ 26 3. Vermilia. “ 8 4. Galeolaria. “ 2 5. Magilus. “ 1 CLASS II. CIRRHIPEDES. ONE FAMILY.