74 Bibliographical Notices. Fig. 2. The tube that runs through the second sexual gland partly unra-velled and freed from its covering : a, inferior aperture, 6, supe-rior aperture of this tube ; the last is situated in the sac at the fore part of the accessory or second genital gland. In this sac above is seen at b the superior aperture of the duct ; here also is c, the inferior aperture of the canal, d. sp., which leads to the spermophore-sac. Fig. 3. Vesicle in which a spermophore lay enclosed ; of this the convo-lutions are partially seen through the walls. Fig. 4. A spermophore unravelled, but broken at one of its extremities, here the upper one. The extremity, a, is represented in the next figure. F^g. 5. The extremity, a, of the last figure, magnified 12 diameters. All the figures except 5 are of the size of nature. BrBLIOGRAPHICAL NOTICES. Shells and their Inhabitants. The Genera of Recent Mollusca ; arranged according to their Organization. By Henry and Arthur Adams. London, Van Voorst, 8vo. Happy the naturalists who have Van Voorst for their publisher ! They shall not want for good printing and first-rate illustrations, and their works shall stand on the same shelf with those of the foremost scientific men of the age. Such was our first thought on turning over the luxurious and costly numbers of this latest book on Conchology. The work is not yet completed, but has so far advanced that we cannot delay noticing it any longer. The first Number was pubhshed on January 1st, 1 853, and at the present time all the Univalves and higher Mollusca have been described, leaving only the Bivalves and Tunicaries to form the subjects of a future notice. As a Manual of the genera of Recent Shells it surpasses all its pre-cursors, both in elaborateness of detail and beauty of illustration. To every one who writes on shells it will be indispensable, and the only thing to be desired is, that it will be used with discretion, and not followed indiscriminately. The work challenges comparison by its promise to supply a want, and we shall best fulfil our task by stating in what respects its guidance is to be distrusted, and spe-cifying some of the points which require emendation. The authors have still the opportunity of making corrections, and will doubtless be obliged to us for making these suggestions ere it is too late. The critical examination of these first 800 pages has proved a rather serious business ; chiefly on account of the strange nomen-clature, and the multiplication and novel arrangement of the genera. All our old conchological notions have been at a discount, and we have had to apply ourselves as to the study of a new art, written in a new language. The number of univalve genera described is about 680, and 437 subgenera. The number of species enumerated exceeds 13,000, being rather less than 20 to each genus, and averaging nearly 1 2 to each genus and subgenus.