110 



PROF. W. A. HERDMAN ON THE DISTRIBUTION 



The following table showing the largest hauls of total Diatoms and 

 of total Copepoda in each of the ten years brings out well how greatly the 

 Diatoms outnumber the Copepoda — in some cases in the proportion of about 

 a thousand to one. 





Diatoms. 



Copepoda. 



Largest haul. 



Date. 



Largest haul. 



Date. 



1907 .... 



698,350 



April 6th 



28,900 



Aug. 17th 



1908 .... 



5,746,300 



May 28th 



68,015 



Sept.. 14th 



1909 .... 



10,358,300 



April 22nd 



71,010 



Oct. 18th 



1910 .... 



70,128,400 



April 22nd 



119,650 



Sept. 19th 



1911 .... 



69,982,500 



May 16th 



248,045 



July 18th 



1912 .... 



202,993,600 



May 30th 



223,789* 



May 20th 



1913 .... 



205,814,700 



May 16th 



118,660 



July 21st 



1914 .... 



155,288,000 



May 4th 



217,571 



Nov. 9th 



1915 .... 



18,893,300 



June 15th 



117,340 



Aug. 2nd 



1916 .... 



24,260,800 



May 25th 



118,524 



Sept. 25th 



1917 .... 



64,339,250 



May 3rd 



147,706 



July 19th 



The relatively high records for Diatoms in 1912 and 1913 are due in the 

 former case to the usual June maximum of Rhizosolenia and Guinardia, and 

 in the latter case to a quite exceptional invasion of Asterionella japonica — 

 the only occasion in our records when this genus has been abundant in the 

 Irish Sea. We regard it as quite a rare form here. It is exceedingly 

 abundant to the south of Iceland (Ove Paulsen) and also in the Gulf of Lyons 

 (Pavillard). 



COPEPODA. 



The following table shows the total numbers recorded of our six important 

 species of Copepoda in the years 1909 and 1910 : — 





1910. 



1909. 



Oithona helc/olandica 



872,678 



465,066 



Psettdocalanus elongatus 



368,326 



309,973 



Acartia clausi 



340,631 



63,373 



Paracalanus parvus 



217,633 



54,120 



Temora longieornis 



147,043 



62,659 



Calamus jinntarchicus . . . 



15,418 



21,412 



* An exceptionally large haul at such an early date — due apparently to several moderately 

 large swarms of different Copepoda occurring together, viz., Calamus, Pseiulocalanus, Temora, 

 and Acartia, 



