132 TEANS ACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



obvious that wide fluctuations occur. The following tempera- 

 ature readings were made on the Lavan Sands cockle beds 

 (between Llanfairfechan and Aber) on September 9th, 1919 : — 



A. Muddy patch with Cardium, etc. abundant, near shore. 2.20 p.m. 



Tide just receded ; sun bright ; strong N.W. breeze. 

 Air temperature 20° C. (just above surface). 

 Sand ,, 1 inch below surface (Cardium stratum) 19-40° C. 



2 inches „ „ „ 18-60° C. 



3 inches ,, (Macoma stratum) 17-00° C. 

 Water „ of stream draining bed, 3 inches deep 21-25° C. 



B. On main cockle bed, almost pure sand ; half-mile from shore. 3 p.m. 

 Air temperature 19-50° C. 



Sand ,, 1 inch below surface 20-00° C. 



2 inches „ 18-50° C. 



3 inches „ 16-80 C. 



The beds at Ynyslas (Dyfi Estuary) were examined 

 during severe frost on February 12th, 1919, when the River 

 Leri was frozen over at its mouth and the foreshore covered 

 with 3 to 12 inches of ice. The cockles were unaffected, but 

 all surface forms (P. stagnalis, Littorina, etc.) buried them- 

 selves and very few cases of Arenicola were noted. Scott* 

 notes the effect of frost in Morecambe Bay resulting in great 

 destruction of cockles and spawn. " The chief cause of the 

 fluctuations of the fisheries for shell fish along the Lancashire 

 coast is due to natural influence . . . the eggs produced 

 by a spawning cockle are fewer in number than is the case with 

 the mussel, and spawning takes place in the early spring. The 

 spat from the bed of cockles may, therefore, be completely 

 destroyed by the sea water becoming suddenly cooled as it 

 flows over the surface of very cold sand." Kelloggf comes to 

 similar conclusions regarding My a armaria, stating that a 

 cold rain when the water is full of swimming larvae may have 

 a disastrous effect, while several days of low temperature may 

 cause it to be more widespread. 



The adverse influence of wind was noted on September 



* A. Scott, " Notes on the Flookburgh Cockle Bed," Report Lancashire 

 Sea-Fish. Lab., 1909. 



t Kellogg, J. L., " Shell Fish Industries," 1910. 



