Eid. hurt a Z2 LASXE os oos ut E 
OF DIATOMS AND COPEPODA IN THE IRISH SEA. 183 
Atlantie species, and all the rest may be classified as temperate neritic. 
Some of these (C. eriophilum, 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 
Oetober. Consequently the genus is well represented throughout a con- 
siderable part of the year, 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, giving 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 
Fic. 6.— Chetoceras decipiens, showing the 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 C. 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 821,811 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 September 
and 100,624 in October. C. debile and C. decipiens were also very abundant 
that October. 
The highest monthly averages for Chetoceras fall as follows during our 
ten years :— 
March <.< in 1907. 
April ... "dn 1909, 1910; and 1912; 
May ... in 1908, 1911, 1913, 1914, 1915, and 1916. 
