54 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



habitat beyond the beach, and that the present vast 

 increase in numbers has been due to some unusual 

 conjunction of circumstances; but what these were I am 

 not yet prepared to suggest. Several possible 

 explanations have occurred to us which we hope to test 

 by further observation. In the case of the Port Jackson 

 Glenodinium plague, Whitelegge thought the increase 

 may have been due to exceptional rainfall and calm 

 weather ; but the occurrence this spring at Port Erin was 

 preceded by unusually dry and rather stormy weather." 



When giving this account of the matter to the 

 Linnean Society, on June 1st, I concluded by saying : — 

 " I am inclined to think that, although I can find no 

 previous record of such an occurrence, it is probable that 

 these swarms of Amphidinium have been seen before at 

 Port Erin, and possibly elsewhere. I fancy I have seen 

 the phenomenon myself in the past, and have supposed 

 it to be due to swarms of Diatoms, which certainly do 

 cause some of the yellowish-green and brownish-green 

 patches on the sand between tide-marks." 



Two days after making this statement I was again 

 on the beach at Port Erin. I found in the same region 

 what was apparently the same patch of discoloured sand, 

 but on examining a scraping with the microscope found 

 that the deposit was now wholly composed of a golden- 

 yellow Naviculoid Diatom — one of the " A?nphisbaena 

 group " of Navicula (fig. 27), probably Navicula 

 (Caloneis) amphisbaena, Bory. I searched the beach 

 carefully between tide-marks, and examined samples 

 from every suspected patch of sand, but could find no 

 trace of Amphidinium. The Navicula, which was present 

 in April in very small quantity (see above) 2 seemed to 

 have completely replaced the Dinoflagellate. We have 

 probably still much to learn in regard to the comings and 



