50 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



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 Dinonagellata. 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 unrecorded 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 Irish Sea during the last five years, and which 

 have been examined in minute detail by Mr. Andrew 

 Scott. 



" Thinking it might be present in the shallow water 

 close to the edge of the beach, Mr. W. Biddell and I 

 took some hauls of the tow-net from a punt worked 

 backwards and forwards in a few inches of water as near 

 as we could get to the discoloured sand, but the 

 gathering, although it contained fine sand and mud, 

 showed no trace of our Dinoflagellate. It may be noted 

 here that although the size of the Amphidinium, 

 005 mm. in greatest diameter, is such that it can slip 

 through the mesh (averaging about 008 mm.) of the finest 



