1904-5. j The Plankton of Thingvallavatn and Myvatn. 1121 
Table II. 
Date of the 
Sample. 
Narrow Race. 
Broad Race. 
Number. 
Per cent. 
Number. 
Per cent. 
1902, July 14 
3 
100 
1903, Feb. 18 
4 
40 
6 
60 
,, March 31 
2 
20 
8 
80 
,, April 16 
3 
23 
10 
77 
„ ,, 30 
15 
60 
10 
40 
,, May 11 
10 
33 
20 
67 
„ „ 31 
10 
50 
10 
50 
,, June 15 
48 
48 
52 
52 
„ „ 30 
20 
51 
19 
49 
Total 
115 
135 
The measurements in Table I. have been taken from specimens 
lying in the preserving fluid, and after treatment with methyl- 
violet ; the breadth of the cell varies then from 4 to 1 1 p. In the 
same manner the 100 specimens in Table III. have been measured, 
hut as the measurements of Rhizosolenias hitherto published by 
different authors generally have been made in dried specimens, I 
have also, for easier comparison, measured 100 specimens of the 
same sample (15th June 1903) in dried condition (Table IV.). The 
figures 4-16 represent the breadth of the cell in p, and each point 
denotes a specimen ; to the right the number of specimens have 
been summed up. In this way we get two curves, which tell us 
several things. 
Table III. Table IV. 
Breadth of the Cell (p), 100 Breadth of the Cell (p), 100 
non-dried Specimens. dried Specimens. 
4 
17 
4. ... 
3 
5 
16 
5. 
7 
6 
11 
6. 
10 
7 
6 
7 
11 
8 
23 
8. 
1 7 
9. . 
11 
9. 
Q 
10 
8 
10 
o 
7 
11 
6 
11 
10 
12. . . 
2 
12 
13 
7 
14. ... 
3 
15. . 
1 
16. . 
1 
PROC. ROY. SOC. EDIN. — YOL. XXV. 
71 
