SEA- FISHERIES LABORATORY. 133 



19th, 1918, while visiting the cockle beds on the Traethmawr 

 (or Traeth Cocos) near Portmadoc. A violent N.W. wind 

 dried the fine surface sand almost as soon as it was uncovered 

 by the falling tide, causing it to drift shoreward in dense 

 clouds. Many cockles became exposed, and soon gaped 

 (owing to relaxation of the muscles), and fine dry sand entering 

 caused their death. 



On one area of muddy sand several acres in extent, and 

 near the mouth of the River Clettwr (Dyfi Estuary), I noted 

 in August, 1915, that only young cockles were present. About 

 three inches below the surface there was a layer of dead shells of 

 all sizes, in all probability the relic of a former bed destroyed 

 by " sanding," and subsequently re- colonised. 



II. Faunistic. 



A mere list (even if annotated) of the animal forms con- 

 stituting the fauna of cockle beds is of little value. Some 

 attempt has, therefore, been made to regard the matter from 

 the ecological standpoint, and some instances of succession of 

 associations will be given, as illustrated by the Dyfi and Lavan 

 Sands. In any locality studied variations may be expected, 

 both as regards the composition of the associations and their 

 extent. The cockle beds may be approached via sand dune, 

 salt marsh, shingle bank or rocky reef, and in the Dyfi Estuary 

 all these occur. Yapp, describes the tidal waters near 

 Ynyslas, as lined by salt marsh, the transitional zones between 

 these and the moor behind being characterised by abundance 

 of Molinia, J uncus maritimus, etc., etc., the succession shore- 

 ward being: (1) Juncetum maritimi, (2) Festucetum rubae, 

 (3) Armerietum maritimae, (4) Glycerietum maritimae, and 

 (5) Salicornetum europaeae, which make up the saltmarsh 

 formation. 



