59 



Mar. 2iicl. — None visible ; very £ew in sample. 



,, 20th. — None visible ; very few in sample. 



,, 23rd. — Faint traces in pools. 



,, 24th. — Patches smaller and fewer but deeper in colour. 



,, 25th. — Only two faint patches in pools. 



,, 26th. — None visible ; fairlj- plentiful in sample. 



,, 27th. — A few small patches. 



,, 30th. — None visible ; fairly plentiful in sample. 

 April 3rd. — None visible : fairly plentiful in sample. 



,, 27th. — Patches very few and fain^. 

 May 2nd. — None visible ; in fair numbers in samples. 



From the above records it appears that during the last six 

 months at least, Ampliidinium has been present on the foreshore 

 at Cullercoats continuously, its entire absence being noted on 

 January 21st and 23rd only, although it has appeared in sufficient 

 quantities to make it conspicuous on only four occasions. Further 

 observations will probably show results similar to those made 

 at Port Erin. Professor Herdman, to whom I wrote on the sub- 

 ject, saj'S, " Amphidinium has appeared off and on in abundance 

 during the last ten years, and is scarcely (if ever) altogether absent. 

 . . . . We have now stopped recording it at Port Erin as it 

 seems to be permanently established on the beach." 



Though we are not yet in a position to make definite state- 

 ments as to the causes of the apparently erratic appearance and 

 disappearance of A. opcrculaium here, it may be of interest to 

 note that on the four occasions on which it is recorded as being 

 visible to the naked eye there have been spring tides ; this is 

 exactly the reverse of Professor Herdman's observations * in 

 1912, when he found that Ampliidinium was most plentiful at the 

 neaps. Mr. Storrow, too, in noting its occurrence in 1913 states 

 that it ''gradually disappeared with the advent of the spring 

 tides." 



I have not observed any alternation of Ampliidinium and 

 Diatoms here {see *), but in one case where a sample of sand and 

 water was kept in the Laboratory for some three weeks, the 

 former, which was visible as a film in the water, sank dowTi after 

 a time and the Amphidinium was found to have been replaced 

 almost entirely by diatoms. It was present, however, at the edge 

 of the jar about J inch below the surface of the sand. 



* " 26th Annual Report of the Liverpool Marine Biological Committee/' 1912. 



