390 PROF. W. A. HERDMAN ON THE OCCURRENCE OF 
only ; and A. opereulatum, which is stated to occur in brackish water on the 
north coasts of Europe. In addition, Kofoid (* Dinoflagellata of the San 
Diego Region,’ 1907) records A. lacustre from fresh water, A. aculeatum, a 
pelagic form from Naples, and A. sulcatum, which he took in a vertical haul 
from 90 fathoms in the Pacific. 
On hunting through the few scattered references to 4. operculatum which 
occur, one finds, however, that К. №. Bergh, in the * Zoologischer Anzeiger? 
for 1882, states (р. 693) that Spengel in December and January found it in 
huge quantities оп the beach at Norderney. Although, therefore, Amphi- 
dinum: operculatum has been recorded once before as occurring in quantity, 
the occurrence appears to be a sufficiently rare event to be worthy of notice; 
and, so far as I can ascertain, the species, although known from several parts 
of North-west Europe, has not been previously found on the British coasts. 
I have written to most of the marine laboratories (Plymouth, Cullercoats, 
St. Andrews, and Millport) and to many marine biologists and have not been 
able to hear of any British record. 
It is, however, not an unknown thing for rare Dinoflagellates to appear 
suddenly in some locality on an occasion in phenomenal quantities. Torrey, 
in the ‘American Naturalist’ for 1902, describes the unusual occurrence of 
a species of Gonyaulaæ on the coast of California. Sherwood and Vinal 
Edwards, in the ‘ Bulletin of the United States Bureau of Fisheries’ for 
1901, tell how for two weeks in September a Pertdinium infested Narragansett 
Bay in such numbers as to colour the water blood-red and cause the death 
of many fishes. 
Finally, Whitelegge, in the * Records of the Australian Museum’ for 1891, 
vives an interesting account of а new species of Glenodinium (G. rubrum) 
which appeared in such quantities in Port Jackson as to give the water “ the 
appearance of blood" and cause the death of great numbers of oysters, 
mussels, and all forms of shore life. Whitelegge supposed that the very 
heavy rainfall that year, by affecting the salinity of the water, and then a 
lengthened period of calm weather which followed, may have provided 
favourable conditions for an unusual development of the Dinoflagellata. 
The Glenodinium appeared in vast numbers about the middle of March and 
disappeared early in May. When it was at its climax, the allied colourless 
species Gymnodinium spirale appeared in the bay and soon increased greatly in 
numbers and became finally even more abundant than the red Glenodinium 
upon which it was evidently feeding. 
Returning now to our Amphidinium operculatum, it is not easy to account 
for the sudden appearance of this unusual Dinoflagellate (previously un- 
recorded in Britain) in such profusion on the beach at Port Erin last April. 
Plankton hauls were being taken regularly across the bay at the time, and 
they showed no trace of the organism. — In fact, Amphidinium has not 
occurred in any of the thousands of gatherings which we have taken in the 
