140 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



having the ventral whorl much expanded. Although 

 the water must contain more of the saline element 

 at Cartsdyke that at Langbank, still there is a great 

 admixture of fresh water, the water at the time of 

 my visit being quite brown with sediment. 



Last summer, while spending a few daj r s at 

 Helensburgh, I noticed that on the shore east from 

 the pier Purpura lapillus was large and strong, like 

 those seen at Langbank and Cartsdyke, and much 

 more so on an average than those found on the 

 shores of Cumbrae and Arran, where the water is 

 purer and less mixed. Thinking it possible that the 

 brackish water might influence the size of the 

 shells, I wrote to my friend Dr. J. R. Henderson, 

 of Granton Marine Station, asking him to send me 

 a few examples of that species from the neighbour- 

 hood of Granton, where I thought the water would 

 be brackish to a degree similar to the Clyde at 

 Helensburgh. I explained the object of my request, 

 that he might better understand what I wanted, 

 and he kindly complied. 



The difference in size, however, was not so marked 

 as at Helensburgh. I had specimens from the four 

 localities — Arran, Cumbrae, Helensburgh, Granton — 

 mounted side by side, the better to illustrate the 

 difference between them; but unfortunately, during 

 removal, the little case containing the specimens has 

 gone amissing, and I have since been unable to find 

 it. These facts, however, many of you may have 

 an opportunity of verifying for yourselves; and the 

 subject is worthy of being followed up with the 

 view of ascertaining what is the cause or condition 

 that disposes these changes to take place, often 

 within a very small radius. On one part of Belfast 

 Lough, the whelk (Littorina littorea) is found having 

 the spire elongated and very much turreted. At 

 Roundstone Bay, Ireland, the calcareous sea-plant 

 Melobesia ttgariciformis is confined to one or two 

 small patches only; and although these have been 

 there for a long series of years, the plant has never 



