OF DIATOMS AND COPEPODA IN THE IRISH SEA. 105 



Atlantic species, and all the rest may be classified as temperate neritic. 

 Some of these (C. criophilum, C. debile, C. decipiens, C. sociale, and C. teres) 

 are spring forms with a maximum in April or May, while C. boreale and 

 C. densum are autumn species having their maxima in September or 

 October. Consequently the genus is well represented throughout a con- 

 siderable part of the 3-ear, and the numbers are very high in April and May, 

 and sometimes also in September and October (see curve, fig. 5). 

 A few of our highest records for the genus, °'ivino' the nearest million 

 in each case, are : — 151 millions on May 4th, 1914, 95 millions on April 29th, 

 1912, 68 millions on May 16th, 1911, 49 millions on April 22nd, 1910, and 

 44 millions on May 19th, 1911. The highest record we have for the autumn 

 species is 30 millions on September 26th, 1912. On May 16th, 1911, 

 C. debile contributed 30 millions and C. sociale 12 millions to the total in the 

 haul ; and on May 4th, 1914, C. debile gave 148 out of the 151 millions 





/ 





Fig. 6. — Chcetoceras decipiens, showing tlie active winter growth. 

 From a photo-micrograph by A. Scott. 



present. If we examine the records of the separate species for the year 1914 

 as an example, we find that 6'. contortum has an average of 62,700 per haul in 

 May, C. debile an average of 867,878 in April and 18,972,800 in May (the 

 record), C decipiens an average of 821,311 in April and 321,050 in May, 

 C. sociale an average of 1,229,500 in May, C. teres an average of 577,867 in 

 April ; while of the autumn species C. boreale has an average of 53,200 in 

 September and 54,644 in October, and C. densum has 151,120 in Septembei 

 and 100,624 in October. C. debile and C. decipiens were also very abundant 

 that October. 



The highest monthly averages for Chcctoceras fall as follows during our 

 ten years : — 



March ... in 1907. 



April ... in 1909, 1910, and 1912. 



May ... in 1908, 1911, 1913, 1914, 1915, and 1916. 



