CORBITLA. 59 



was established on a single specimen " taken from the 

 root of a fucus cast ashore at Ballaugh/' Dr. Morch 

 gave me the same species, which he had procured from 

 Greenland. It is undistinguishable from C. mediter- 

 ranea, except in its much larger size and the absence of 

 coloured streaks ; in shape, sculpture, and peculiar den- 

 tition it corresponds exactly with the Irish specimens, 

 and with some from the Gulf of Lyons, for which I am 

 indebted to the kindness of M. Martin. I cannot help 

 conjecturing that the Manx shell might have been 

 brought to this country with others from the Arctic 

 seas, and have afterwards become accidentally mixed in 

 Forbes' s collection; especially when I remember that 

 he sent me about the time of his publishing the 

 ' Malacologia/ and when he was almost a tyro in British 

 conchology, another shell for my opinion. This was 

 Venus fluctuosa, a native of the North- American seas. 

 The memorandum accompanying the last-mentioned 

 shell stated that it had been received by Forbes, as 

 picked up on the shore at Leith, but not by himself. 

 The difference of size between Greenland and Mediter- 

 ranean specimens of the same species further exemplifies 

 my remarks in the first volume on this subject. 



The late Dr. Lukis sent me specimens of C. labiata, 

 a handsome South- American species, with which the 

 tide-mark in a small bay in Guernsey had been strewn 

 in November 1859, immediately after the wreck of a 

 ship in ballast from Buenos Ayres. Along with this 

 Corbula were found a small Melania and other tropical 

 shells. This shows the importance of carefully studying 

 the geographical distribution of the Mollusca, in order 

 to avoid errors likely to result from accidents of the 

 above kind. Otherwise all these shells might be de- 

 scribed or enumerated as British. 



