54 TRAXSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



habitat bevoiid the beach, and tliat the present vast 

 increase in numbers has been due to some unusual 

 conjunction of circumstances; but what these were I am 

 not vet prepared to sug'g'est. Several possible 

 explanations have occuried to us which we hope to test 

 by further observation. In the case of the Port Jackson 

 Glenodiniuni 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 Amyhidininm have been seen before at 

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

 the phenomenon myself in the past, and have sup])Osed 

 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 Xaviculoid Diatom — one of the '" A in pliishtioia 

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

 {C alone is) ampliishaena, Bory. I searched the beach 

 carefully between tide-marks, and examined samples 

 from everv suspected ])atc}i of sand, but could find no 

 trace of AinphnlinivDi . 'I'lic Xavicula, wliich was present 

 in April in very small cjuantity (see above), seemed to 

 have (■()in])lcte]y rejdaced the Dinoflagellate. We have 

 proba])ly still nnicli \o learn in regard lo <be comings and 



