OF NORTHUMBERLAND AND DURHAM. 99 
science, to adhere in the main to some system 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 nomenclature 
of natural history, which makes it necessary to examine into the 
priority of each individual synonym 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 Lovén, of 
Stockholm, entitled “ Index Molluscorum litora Scandinaviz 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- 
neean species; an assistance which his laborious and critical ex- 
amination of the Linnean 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 completed 
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 Oirrhipoda, and the Yestaceous 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 Zoophytes, the second to Crus- 
tacea, and the third to Annelida. 
* Mr. Hanley is about to publish the results of this examination in a work 
exclusively devoted to the species preserved in the cabinet of Linnzus, the 
value of which every naturalist must appreciate. 
