The common works upon this subject, however, will appear to every person of science very essentially defective, inasmuch as the _relation_ of the animal and shell, with their dependence upon each other, is a radically important consideration in the examination of either. Neither, in the attempt to obviate this difficulty, is a work upon Malacology at large necessarily included. Shells, it is true, form, and, for many obvious reasons, will continue to form, the subject of chief interest, whether with regard to the school or the cabinet; still there is no good reason why a book upon _Conchology_ (using the common term) may not be malacological as far as it proceeds. In this view of the subject the present little work is offered to the public. Beyond the ruling feature—that of giving an anatomical account of each animal, together with a description of the shell which it inhabits,—I have aimed at little more than accuracy and simplicity, as far as the latter quality can be thought consistent with the rigid exactions of science. No attention has been given to the mere _History_ of the subject; it is conceived that any disquisition on this head would more properly appertain to works of ultimate research, than to one whose sole intention is to make the pupil acquainted, in as tangible a form as possible, with _results_. To afford, at a cheap rate, a concise, yet sufficiently comprehensive, and especially a well illustrated school-book, has been the principal design. In conclusion, I have only to acknowledge my great indebtedness to the valuable public labors, as well as private assistance, of Mr. Isaac Lea, of Philadelphia. To Mr. Thomas Wyatt, and his late excellent _Manual of Conchology_, I am also under many obligations. No better work, perhaps, could be put into the hands of the student as a secondary text book. Its beautiful and perfectly well-coloured illustrations afford an aid in the collection of a cabinet scarcely to be met with elsewhere. E. A. P. PREFACE TO THE SECOND EDITION. In issuing a second edition of this “Conchology,” in so very brief a period since the publication of the first large impression, the author has little more to do than to express the high pleasure with which he has seen his labors well received. The success of the work has been decided; and the entire design has been accomplished in its general introduction into schools. Many important alterations and additions are now made; errors of the press carefully corrected; many more recently discovered American species added; and the work, upon the whole, is rendered more worthy the public approbation. E. A. P. INTRODUCTION.