PURPURA LAPILLUS. 139 



XII. 



JOTTINGS FROM MY NOTE-BOOK. 



BY DAVID ROBERTSON, F.L.S., F.G.S. 



Purpura lapillus, Lin. 



[Read 8th June, 1886.] 



I find among some of my jottings made fourteen 

 years ago, that on the shores of the Clyde at 

 Langbank, where the river has a great admixture 

 of fresh water, very large sized shells of this mollusc 

 were found ; and although not one was found living, 

 the dead shells were moderately plentiful among the 

 stones near high -water mark. 



When, it may be asked, did these molluscs live ? 

 Neither Forbes nor Jeffreys makes any mention of 

 this species occurring in brackish water ; and it was 

 therefore thought that it must have lived at a time 

 when that part of the river was less subjected to 

 the influence of fresh water than it is now. 



As the post - tertiary fossiliferous clays stretch 

 alonsr the side of the river both above and below 

 this point, it was thought possible that these shells 

 mijrht have been washed out from some of the older 

 clays. The post-tertiary beds of the Clyde, however, 

 contain very few examples of this shell : and it is a 

 rare occurrence to find even one of them in the 

 clays. It is also to be remarked that none of the 

 other shells belonging to the clays were seen strewn 

 along the shore at this point, whereas they might 

 have been expected to occur in a much greater 

 number. 



Some time afterwards I examined the shore near 

 the dry-dock at Cartsdyke, a few miles further down 

 the river, and found Purpura lapillus in abundance 

 and living. The shells were large, many of them 



