68 



The drier portions of the beach were free from the brown 

 patches, but from one of these a scraping of sand was taken about 

 IJ inches deep, brought into the Laboratory and covered with 

 filtered sea water. Next morning the surface of the sand was 

 covered with Amyliidinium. 



During the same day, December Isb, a thorough examination 

 of the beach w^as made again. The sand in the pools w^as now 

 more thickly covered with the bro^\al films, which were becoming 

 buoj^ed up in the water and leaving the sand altogether in many 

 cases. The patches were still as prevalent on the beach from end 

 to end of Cullercoats Bay, but there was no sign of the Amphidinium 

 on the Tj^iemouth sands or beyond the northern breakwater. 



These and further observations continued up to the time of 

 writing (May, 1918) are not in accord with Whitehead's explana- 

 tion that the Amphidinia sink into the sand when covered with 

 water — in fact, the reverse is the case, for whenever w^ater was 

 present on the surface the brown patches occurred, while they 

 were entirely absent from the drier regions. That the Amphi- 

 dinia sink into the sand when it becomes dry is shown from the 

 result of moistenmg the scrapings of drier sand. 



On December 2nd, the Amphidinium had diminished some- 

 what in quantity, and on the 3rd had vanished entirely. The 

 total disappearance may have been due to some extent to a heavy 

 gale which occurred during the night. 



From December, 1917, until May, 1918, the records of the 

 occurrence of A . operculatum in Cullercoats Bay are as f oUows : — 



Dec. 1st. — Plentiful on wet sand ; thick film in pools. 



,, 2nd, — Decreased in quantity. 



„ 3rd. — Disappeared. 



„ 6th. — Present in small quantities. 



,, 8th. — Disappeared. 



,, 13th. — Plentiful on sands and in pools (spring tides). 



,, 14th. — More plentiful. 



„ 15th. — Heavy films in pools ; disappeared from sands, present 

 in scrapings. 

 Jan. 5th. — None visible. 



„ 21st. — None visible \ Very severe weather; entirely absent 



,, 23rd. — None visible. / from scrapings and water samples. 



Feb. 9th. — None visible. 



„ 14th. — None visible ; very scarce in samples. 



,, 20th. — None visible ; rather more plentiful in samples. 



,, 21st. — None visible; rather more plentiful in samples. 



„ 25th — None visible ; none from examination of samples ; two 

 individuals obtained by centrifuging 8 ccs. of watei. 



,, 26th. — None visible ; very few in sample. 



„ 28th. — None visible ; verj^ few in sample. 



