The physical characteristics of the Bay having been set out in the preceding paper, it will not be necessary to repeat that description here, since only special local featureswill be dealt with, as occasion arises. Peculiarities of distribution had been noted for the Trochidæ and Littorinidæ, and it was with a view to obtaining further information as to the operation of local littoral conditions and their effects upon the fauna that these grouops were more particularly examined. These notes detail some of the peculiarities, and outline what are believed to 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, observed 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 Llanrhstyd, some eight miles south of Aberyswyth, to Mochras, a few miles south of Harlech. Some observations 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 the south, the most southerly being some miles below Cemmæs Head.