INVESTIGATION OF THE PLANKTON OF THE IRISH SEA. 163 
| | | 1 
| | Greatest | | | 
Date | No. | Vol. | per cent. | Diato Dinofla- | Cope- Cope- | 
Nu | of | inec. | deviation dito. gellates poda pod | | 
epth. | hauls. | average. from ditto. ditto. | Nauplii. 
| | average. | 
April 3— | -52 | —49  -14 | —19 
8 fathoms | 6 0:2 0 | 
| +24 +24 +21 +39 
Apil6— | (-1 | =51 | =53 | -50 | -4 
20 fathoms | 5 0:58 | | 
+ 3 +41 +56 +42 +41 | 
April 8— —23 | —34 | -20 —40 | -39 | 
20 fathoms 6 0:52 | | | | 
+15 417 +15 | +22 | +22 
April 13— | (-l7 —41 —65 | —22 | —57 
8 fathoms 5 0:48 | 
| +25 +73 +440 +53 +129 | 
May 25— | —10  -21 | —22 | -72 | -33 
20 fathoms 4 16:125 | ¢ | | 
+21 +15 +23 +60 | +56 
August i - 10 —27 —13 — 21 
20 fathoms 4 0:5 0 | 450 4a ao | Lo 
Oe í oZ 
September 16 — 26 — 36 — 22 | —36 | —3l 
20 fathoms 4 6:1 | | 
+23 +30 96 | +53 | +87 
| | 
In all there are about 50 species of organisms that occur with fair 
regularity throughout the series : 24 species of diatoms, 4 of dinoflagellates, 
8 of Copepoda, and about 14 other organisms or groups of organisms which 
are not of so much importance and may be omitted. Of the 24 species of 
diatoms, as a general rule, if a species occurs in one of the hauls of a series 
it occurs in all, and in many cases in much the same proportions in all— 
that is, there may be two or three or even more times as many individual cells 
in one haul as in another, but all will be in the tens, or in the hundreds, or 
the thousands, or millions. For example, on April 3rd we have : — 
Coseinodiseus radiatus, 1600, 2600, 2600, 2800, 2800, 2200. 
Streptotheca thamensis, 40, 30, 40, 40, 60. 
Many other similar examples might be given from the detailed records, but, 
on the other hand, other occasions show more variation. It is much the 
same with the four common species of dinoflagellates recorded. There, again, 
we find cases of considerable constancy in the hauls of a series, such as :— 
May 25th—Peridinium divergens, 46000, 62000, 50000, 44000 ; 
