OF NORTHUMBERLAND AND DURHAM. O 



science, to adhere in the main to some syst^xi already established, 

 rather than to introduce changes that may not stand the test of 

 further experience. 



A spirit of rigid criticism is now abroad on the nomenclatUTe 

 of natural history, which makes it necessary to examine into the 

 priority of each individual synonyra in the genera and species. 

 This we have done to the best of our ability and means; and we 

 must acknowledge the great assistance we have derived in this 

 respect from the excellent little Synopsis of the Swedish and 

 Norwegian Mollusca lately published by Professor Loven, of 

 Stockholm, entitled " Index Molluscorum litora Scandinavise Oc- 

 cidentalia habitantium." as well as from his obliging communi- 

 cations. Our acknowledgments are equally due to Mr. Sylvanus 

 Hanley for his kind assistance in identifying several of the Lin- 

 naean species ; an assistance which his laborious and critical ex- 

 amination of the Linnoean Cabinet renders him peculiarly able 

 to afford.* 



Had there been any work which we could have taken as a 

 text book, our task in drawing up this Catalogue would have 

 been comparatively light, but at present no such work on Bri- 

 tish Mollusca exists, though the desideratum is in the course of 

 being supplied by the " History of British Mollusca and their 

 Shells" by Professor E. Forbes and Mr. Hanley, one or two parts 

 of which have already appeared ; but as it will not be comj)leted 

 for three years, we shall not be able to avail ourselves of it on 

 the present occasion. 



As our Catalogue is exclusively confined to the Mollusca, three 

 classes of Testaceous animals that have usually appeared in British 

 works on shells do not find a place in these pages ; these are, the 

 Foraminifera, the Cirrhq:)oda., and the Testaceous Annelida. 

 Modern investigations have proved that these belong to entirely 

 different departments of the animal kingdom, to which they 

 must now be assigned — the first to Zoo2ohytes, the second to Crus- 

 tacea, and the third to Annelida. 



* Mr. Hanley is about to publish tlie results of this examination in a work 

 exclusively devoted to the species preserved in the cabinet of Linnreus, the 

 value of which every naturalist must appreciate. 



