470 Mr. W. Clai-k on the Classification of the 



dissection and examination of the marine testaceous moUusca. 

 Nearly every animal that is^ or may be mentioned in the ' Annals/ 

 or appear in a distinct work, has undergone in a living state my 

 personal examination, and in many species often repeated. I 

 have had my own dredger, and I may say with some confidence, 

 that there are few individuals who have had better opportunities 

 of observing the organs, their functions, and the habitudes of these 

 varied and interesting animals, than myself. I trust that my dis- 

 sections and investigations will give such a general, and in some 

 measure particular account of their external configuration and 

 internal anatomy as will suffice to give the younger students of 

 this branch of zoology an adequate knowledge of their organiza- 

 tion, to afford them sufficient aid to discriminate the organs of the 

 animals, so as to let none pass without careful observation ; for 

 how many curious creatures, which perhaps only occur once in a 

 lifetime, have been overlooked for want of such assistance, and 

 are for an indefinite time lost to science ! I speak with deep regi-et 

 on this point ; as in my earlier career I have neglected opportu- 

 nities that have never, occurred since, and which I have felt the 

 loss of. 



The detailed anatomies of Pholas dactylus, Teredo megotara, 

 Dentalium tarentinum, Bulla hydatis, and other desultory ana- 

 tomical observations by myself, with references to M. Cuvier, the 

 " principium et fons" of faithful comparative anatomy, will suf- 

 ficiently explain the structure of the Acephala and Gasteropoda 

 that have been treated of in these memoirs; which are byno means 

 to be considered as strictly local ones. Though the species have 

 been obtained from one vicinity, they will be found to give, with 

 others which will speedily follow in a more collected form, I hope, 

 a faithful portraiture of most of the animals of the entire class of 

 the British marine testaceous MoUusca. There are however gaps 

 which it has never been in the power of malacologists to till up ; 

 but the hope of acquiring the rare desiderata ought not to be 

 considered as forlorn. I have lately fallen in with very unex- 

 pected acquisitions which afford a practical illustration of the 

 quotation — 



" Tiime, quod optanti Divum promittere nemo 

 Auderet, volvenda dies, en ! attulit ultro." 



I may mention that these remarks were scarcely dry, when I 

 received from Exmouth a pine log full of magnificent Teredo me- 

 gotnra alive, which species I had not seen for thirty years, and 

 enabled me to supply the anatomy of the Teredines. 



