XXXU INTRODUCTION. 



We have enumerated and characterized ninety British 

 Nudibranchiate and Pellibranchiate Gasteropoda. Of these 

 more than two-thirds have as yet been noticed only in the 

 British seas. It is quite impossible to institute any com- 

 parison of this portion of our fauna with the accounts of 

 the corresponding- portion of any extra-British fauna, since 

 the minute and elaborate researches of Messrs. Alder and 

 Hancock have given us an overwhelming advantage. 



Our single marine naked pulmonated Mollusk is not 

 known at present, we believe, out of the Celtic province ; 

 but, as it has been seldom sought for, may have escaped 

 notice. Our two testaceous marine Pulmonifera range 

 southward of Britain, and one of them is found on the 

 opposite shores of the Atlantic. 



Our fourteen species of Ceplmlopoda are, with one ex- 

 ception, found beyond our limits. At least four of them 

 may be regarded as common to all the seas around us, 

 whilst six are apparently immigrants from more southern, 

 and three from more northern provinces. There are still 

 hopes of our acquiring, in the course of natural history 

 research, a few additions to our list in this interesting 

 portion of the fauna, one that has been in a great measure 

 neglected. The interesting and curious genus OnychoteutMs 

 especially may be expected to furnish a British re^iresen- 

 tative. We would urgently press upon our younger na- 

 turalists to let no cuttle-fish pass unexamined. 



Our land and fresh-water Mollusks present but few pecu- 

 liarities, and are almost all continental. The Helix fusca 

 was supposed to be exclusively British, and is stated to be 

 so in our text, but it appears now that the shell referred 

 to under the name of Helix revelata (a very distinct species) 

 by Bouchard Chantereaux is really fusca. It is indeed 

 very doubtful whether any of our land shells can be 



