PEEFACE 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 Q 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 (Am- 

 monoidea) P. Fischer QManuel de Conchyliologie^ 1887). In 

 the Gasteropoda the outlines are those adopted by Pelseneer 

 (Mem. Soc. Malacol. Belg. xxvii. 1894), while the details are 

 derived, in the main, from P. Fischer. The Amphineura, how- 

 ever, 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. 



Acknowledgment of the principal sources of information 

 has been made in footnotes, and a short list of leading author- 

 ities has been appended to the chapters on anatomy, for the use 

 of students desirous to pursue the subject further. In the case 



