102 



i>ROi\ W. A. HEhDMAK ON THE DISTRIBUTION 



Laboratory, finds that as a matter of fact this form did appear in abundance 

 in the collections of October 1909, within a month of the time when 

 according to our records it reached Port Erin. Whether or not this species 

 was brought accidentally by a ship from the far East, there is no doubt that 

 it was not present in our Irish Sea plankton gatherings previous to 1909, 

 but has been abundant since that year, and has completely adopted the 

 habits of its English relations — appearing with B. mobiliensis in late autumn, 



Fig. 3. — Photo-micrograph of a plankton preparation showing (a) Biddidphia 

 mobiliensis, forma " regia," and (b) B. si?iensis. 



persisting during the winter, reaching a maximum in spring, and dying out 

 before summer. Biddidphia is generally the first Diatom to show a marked 

 increase in early spring, and is responsible for the moderate rise in the curve 

 which takes place in February or March. 



Our largest records of Biddidphia are as follows : — 



From three hundred thousand to over six hundred thousand per haul on 

 several occasions between middle of March and middle of April in 1910 and 

 1911, and towards end of April and beginning of May, 1916. 



From three hundred thousand to over seven hundred and fifty thousand on 

 ten occasions between November 10th and 27th, 1911, 1914, and 1915. 



The highest monthly averages in the early spring months occur as 

 follows : — 



February ... in 1907 and 1912. 



March .. in 1910, 1911, 1914, and 1915. 



April ... in 1908, 1909, 1913, and 1916. 



A second, usually slighter, maximum occurs in November, when the 

 numbers are higher than in December and January ; but on three occasions 



