212 THE DISPERSAL OF SHELLS. 



In the "British Conchology/' in 1862, Mr. Jeffreys 

 expressly inclined to a belief that the creature ought to 

 be looked upon as a native of Britain, and of the whole 

 of the North of Europe, adding that if, as he believed, 

 "the indigenousness of the Dreisscna as regards this 

 country should hereafter be established, the ingenious 

 theories which have been put forward to account for the 

 mode of its transport across the seas will not require 

 further discussion." The circumstance of its not having 

 been noticed here before 1824, and then only in a 

 metropolitan locality, he remarked, did not preclude the 

 possibility of its having previously existed in some 

 other part of the country, its not having been previously 

 recorded as British rather proving a want of observation 

 or opportunity than its non-existence. As tending to 

 confirm this belief, he pointed out — that Helix cartitsiana, 

 H. ohvohUa and Claiisilia rolphii, '' all of which are con- 

 spicuous land-shells," were unknown to the observant 

 Montagu, although not uncommon in some parts of this 

 country, and clearly indigenous, and many similar 

 instances might be cited, he said, on this point, as well 

 as with respect to the sudden and unaccountable 

 appearance and disappearance of certain species in 

 particular spots : that the Pinna fluviatilis of Sander 

 was doubtless our Dreissena, which was therefore found 

 in the interior of Germany before 1780, inhabiting 

 streams which flowed into the Rhine : that in draining 

 the Lake of Haarlem, which apparently never com- 

 municated with any port or harbour, it was found in 

 abundance, and it had been discovered, also, in an 



