INTRODUCTION. XXV 
A. Coast REGIon. 
(1). Muppy Sait Mars Formation. 
Muddy salt-marshes occur at the mouths of the rivers. The 
extreme conditions of life on the seaward side explain the 
paucity of their molluscan fauna. Littorina rudis, Maton, and 
Paludestrina stagnalis, Baster (= Hydrobia ulve, Pennant) 
occur in large numbers associated with halophytic plants such 
as Salicornea europea, Linné; Glyceria maritima, Mert and 
Koch, and Trigiochin maritimum, Linné. On the landward 
side conditions are less unfavourable, the mud is seldom tide- 
washed, and the water is usually fresh. In the marshes and 
rhines, which are brackish during very high tides, Limnea 
truncatula, Muller, occurs in great numbers, its frequency is 
very noticeable during dry summers, when the water in the 
rhines is low. The strong rush of water up the river mouths 
frequently carries Macoma balthica, Linné; Littorina obtusata, 
Linné ; Littorina rudis, Maton, and others, considerable dis- 
tances inland. 
Phytiamyosotis, Draparnaud, and Ovatella bidentata, Montaau, 
are frequent under stones just above high water mark at the 
mouths of all the tidal rivers. 
(2). Dune Formation. 
The sand dunes are frequented by an interesting association 
of a few species, the individuals of which often occur in 
enormous numbers. Amongst the strand plants of the fore- 
shore ( Atriplex hastatu, Linné; Salsola Kali, Linné, and other 
representatives of the Chenopodiacez) dead shells of H. aspersa, 
Muller, and H. virgata, da Costa, chiefly occur. Behind the 
foreshore there is an association of plants (see Plate I, fig. 1) 
with sea-couch grass (Agropyron junceum, Beauv.) the dominant 
one, and the sand sedge (Carex arenaria, Linné) the sub- 
dominant. Amongst these we find 
