1904-5.] The Plankton of Thmgvallavatn and Myvatn. 1167 
Explanation of Plate II. 
Figs. 1-3. Rhizosolenia eriensis, H. L. Smith : — 
1. Large cell, with the plasma concentrated near the one 
end, where the rest from the last division is seen. 
2. Part of a cell with resting spore. 
3. Resting spore of another cell, seen from the narrow side. 
Figs. 4-5. Rhizosolenia paludosa, 0. Zacharias : — 
4. A whole cell. 
5. Newly finished cell-division, the two daughter cells 
cohering. 
Figs. 6-8. Melosira italica, Kiitz. ; parts of different chains with 
auxospores. 
Figs. 9-10. Mallomonas sp. : — 
9. Vegetative cell with setae. 
10. Spore-bearing cell without setae. 
Fig. 11. Cosmarium phaseolus, Breb. ; the same cell in front and 
in vertical view. 
„ 12. Staurastrum pelagicum , West and G. S. W. ; in front 
and in vertical view. 
,, 13. Staurastrum brevispinum, Breb.; in front and in vertical 
view. 
,, 14. Staurastrum paradoxum, Meyen, forma; in front and in 
vertical view. 
,, 15. Staurastrum Bieneanum , Rabenh., forma; in front and 
in vertical view. 
Figs. 16-17. Stellate colonies of Synedra acus, Kiitz., var. delica- 
tissima, (W. Sm.) Grun. ? 
Fig. 18. Peridinium aciculiferum , Lemmerm. ; cell in ventral 
view, showing the arrangement of the plates ; under- 
neath the three prominent ridges (forming the spines) 
seen from the antapex. 
The magnifications are as follows : — 
Figs. 1—5, 8, 18, objective P25 x 2*5 mm. Comp, ocular, 8 
(Water immersion.) 
„ 6, 7, 9-15, objective 0'95 x 4*0 mm. Comp, ocular, 8 
, 16,17, ,, 0'65x8'0 mm. „ 8 
( Issued separately , January 5 , 1906 .) 
