Transcriber’s Note: This work features some large and wide tables. These are best viewed with a wide screen. THE CAMBRIDGE NATURAL HISTORY EDITED BY S. F. HARMER, M.A., Fellow of King’s College, Cambridge; Superintendent of the University Museum of Zoology AND A. E. SHIPLEY, M.A., Fellow of Christ’s College, Cambridge; University Lecturer on the Morphology of Invertebrates VOLUME III [Illustration] [Illustration: Map to illustrate THE GEOGRAPHICAL DISTRIBUTION of the LAND OPERCULATE MOLLUSCA] _The figures indicate the number of known species._ MOLLUSCS By the Rev. A. H. COOKE, M.A., Fellow and Tutor of King’s College, Cambridge BRACHIOPODS (RECENT) By A. E. SHIPLEY, M.A., Fellow of Christ’s College, Cambridge BRACHIOPODS (FOSSIL) By F. R. C. REED, M.A., Trinity College, Cambridge New York MACMILLAN AND CO. AND LONDON 1895 _All rights reserved_ “Why, you might take to some light study: conchology, now; I always think that must be a light study.” GEORGE ELIOT, _Middlemarch_. COPYRIGHT, 1895, BY MACMILLAN AND CO. Norwood Press: J. S. Cushing & Co.--Berwick & Smith. Norwood, Mass., U.S.A. PREFACE TO THE MOLLUSCA The general plan of classification adopted in this work is not that of any single authority. It has been thought better to adopt the views of recognised leading specialists in the various groups, and thus place before the reader the combined results of recent investigation. This method may, perhaps, occasion a certain number of small discrepancies, but it is believed that the ultimate effect will be to the advantage of the student. The classification adopted for the recent Cephalopoda is that of Hoyle (‘Challenger’ Reports, _Zoology_, vol. xvi.), for the fossil Cephalopoda (Nautiloidea) that of Foord (_Catalogue of the Fossil Cephalopoda in the British Museum_, 1888–91), and (Ammonoidea) P. Fischer (_Manuel de Conchyliologie_, 1887). In the Gasteropoda the outlines are those adopted by Pelseneer (_Mém. Soc. Malacol. Belg._ xxvii. 1894), while the details are derived, in the main, from P. Fischer. The Amphineura, however, have not been regarded as a separate class. The grouping of the Nudibranchiata is that of Bergh (Semper, _Reisen im Archipel der Philippinen_, ii. 3). The Pelecypoda are classified according to Pelseneer’s most recent grouping.