OF DIATOMS AND COPEPODA IX THE IRISH SEA. 



109 



point in September — tbe greatest recorded monthly average being 10,967 for 

 September 1912. It is interesting to notice that according to Pavillard 

 Guinardia flaccida is abundant in the Gulf of Lyons as late as October. 



\1 



m 



A\ 



i 



' KM* 



Fig. 10. — Guinardia flaccida, from a photo-micrograph by A. Scott. 



Table 

 showing the month!)/ averages of the selected Diatoms throughout a year. 



1912. 



Bidditlphia. 



Chcetoceras. 



Coscino- 

 discus. 



Rhizosolenia. 



Thalassi- 



osira. 



Guinardia. 



Lauderia. 



Jan 



24,920 



7,342 



9,877 



22 







257 



189 



Feb. . . 



36,885 



10,301 



10,034 



12 







105 



i 



Mar. . . 



21,176 



3,977,292 



95,446 



525 



25 



162 



337 



Apr. . . 



21,869 



18,365,750 



100,619 



:56,464 



721,338 



3,158 



1,622,478 



May .. 



1,072 



2,844,861 



14,586 



22,008,744 



41,033 



2,789,433 



170,878 



June . . 







67,543 







40,833,771 







5,919,429 







July .. 







39,527 



56 



1,228 







158 







Aug. . . 



11 



694,961 







13 















Sept. . . 



4,131 



7,702,658 



1,077 



117,122 



3,978 



10,907 



8,944 



Oct 



5,827 



214,421 



11,914 



820 



57 



2,176 



29 



Nov. . . 



25,714 



9,476 



5,436 











21 







Dec. . . 



8,059 



1,106 



1,573 











141 







The above table shows very clearly how these important genera reach 

 their maxima at different times, and how, for example, Chastoceras in spring 

 (April) gives place to Rhizosolenia and Guinardia in early summer 

 (May and June). Curves can be drawn mentally from a glance at 

 the columns of figures which will demonstrate the waxing and waning of 

 the several types, 



