1904 - 5 .] The Plankton of Thingvallavatn and Myvatn. 1099 
1903, samples have been sent me from a small lake near Ivigtnt, but 
these samples contained only mud and bottom organisms and no 
plankton at all ; consequently they did not suit my purpose. 
With regard to the Icelandic plankton, I had the good luck to 
find the right man for an undertaking of this kind. It was the 
Icelandic naturalist, Mr B. Soemundsson, assistant teacher at the 
classical school in Reykiavik, who in several ways has promoted 
our knowledge of the Icelandic fauna. Hear the Thingvallavatn he 
found a young man, Mr Simon Pjetursson, whom he could re- 
commend as being capable of undertaking my task. Furthermore, 
he interested the Dean of Skutustodum, the Rev. Arni Jonsson, 
who resides near Myvatn, in the plankton explorations. Two men 
from his parsonage have procured the samples from this lake. 
It had, of course, been my intention to have the collections made 
simultaneously from both of the lakes, hut a sad accident prevented 
this. All the apparatus which first were sent to the Rev. A. 
Jonsson were, while on the way to Myvatn, according to a letter 
from him, destroyed by a great fire in the town of Husavik. Hew 
apparatus had therefore to be sent to Skutustodum, but these 
did not reach their destination until some nine months later. 
The explorations in Thingvallavatn were at that time already 
commenced. 
On the Thingvallavatn the samples have been collected from 
14th July 1902 to 30th June 1903 ; on the Myvatn from 
1st April 1903 to 2nd April 1904. Only qualitative nets have 
been used for the explorations, and nearly all the samples are 
surface samples ; from Thingvallavatn I have some summer samples 
from deep water. The samples have been taken with two 
different nets, the one Miillergauze Ho. 20, and the other my 
Bosmina net (Griesgauze Ho. 60). Only Crustacea and some of 
the Rotifers could be gathered in this last net, but no phytoplank- 
ton. The gatherings from Ho. 20 were preserved in formaline, the 
gatherings from the Bosmina net in alcohol. The tp. of the air and 
that of the surface water were taken by a centigrade thermometer 
of a very ordinary construction. In winter, when one of the 
lakes was ice-bound, samples were taken through a hole in the ice. 
It must be considered that the method used was only a very 
primitive one, but it must be remembered that all the samples 
