254 THE DISPERSAL OF SHELLS. 



established itself in the above locality. The four 

 living specimens mentioned are the only ones (other 

 than those intentionally introduced or their de- 

 scendants) which have been detected in these islands, 

 and the name of the species has very properly been 

 omitted from the new list of 1892. Mr. Collier and 

 Mr. Rogers, as stated in 1884, visited Cardiff soon after 

 the finding of Mrs. Robertson's specimens, but, although 

 they found the exact spot in which the creatures had 

 been picked up, they failed to discover other speci- 

 mens, and came to the conclusion that those originally 

 found were ballast shells, the moor being the " place 

 where all the ballast is put." Mr. Wotton, in 1886, 

 mentioned that the original shells were found near a 

 small patch of raised ground, covered with ballast-plants, 

 where the H. cartusiana^ no doubt accidentally intro- 

 duced, was formerly known to occur. He had searched 

 closely very many times for H. vtilosa, but without 

 success ; the creature had certainly been imported, he 

 thought, probably with ballast, or possibly with Esparto 

 grass, large quantities of which are brought into Cardiff 

 and stored on the moors. A brickyard, he added, 

 '* now covers the spot where H, villosa was taken, and 

 various works and docks are fast occupying the 

 ground." About forty years ago, as already noticed, 

 Canon Tristram turned loose, on a moor in co. 

 Durham, several specimens which he had brought 

 alive from Switzerland, and they or their posterity 

 were ascertained to be living in the same place ten 

 years afterwards. The Rev. J. W. Horsley, also, has 



