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The Distribution of some Littoral Trochidse and 

 Littorinidse in Cardigan Bay. 



By 

 Chas. L. Walton, 



University College of Wales, Aberystivyth. 



The physical characteristics of the Bay having been set out in the pre- 

 ceding paper, it will not be necessary to repeat that description here, since 

 only special local features will be dealt with, as occasion arises. Peculiari- 

 ties of distribution had been noted for the Trochidee and Littorinidse, 

 and it was with a view to obtaining further information as to the opera- 

 tion of local littoral conditions and their effects upon the fauna that 

 these groups were more particularly examined. These notes detail some 

 of the peculiarities, and outline what are believed to be the controlling 

 causes, at any rate for the central area of the Bay. It would be of great 

 interest to know whether similar peculiarities have been, or can be, 

 ob&erved for other areas of coast. The region discussed lies between 

 Gwbert-on-Sea at the mouth of the Teifi, to the south ; and a point a 

 few miles beyond Pwllheli to the north. The portion more closely 

 examined extends from near Llanrhystyd, some eight miles south of 

 Aberystwyth, to Mochras, a few miles south of Harlech. Some observa- 

 tions were also made about Portmadoc, Borth-y-Gest, and Pwllheli in 

 the northern part of the Bay ; and about New Quay, and the mouth of 

 the Teifi. to the south, the most southerly being some miles below Cemmses 

 Head. 



Much of the coast is difficult of access, and the investigation has been 

 going on for a number of years. 



The following species have been observed living within tide marks : — - 



Trochid.e. 



(1) Gihhula cineraria (Linnaeus). 



(2) G. umhilicata (Montagu). 



(3) G. magus (Linnaeus). 



(4) Monodonta crassa (Montfort). 



(5) CaUiostotna zizyphinus (Linnaeus). 



