1136 Proceedings of Royal Society of Edinburgh. [sess. 
The second generation will produce two parthenogenetic broods 
and then ephippia. The first of these broods will also, to begin 
with, propagate parthenogenetically (August-September), and later 
on sexually (October-December) ; the second one only sexually 
(November-December). The first of these broods lives from July 
to December, and is in December represented by large females 
with ephippia and short spines ; the second brood, which lives 
from September-October to December, is in December represented 
by the small-sized, loug-spined, ephippial females. 
With regard to the above given details, there is especially one 
doubtful point. I have not been able to decide whether the first 
generation totally disappears in the latter part of August, or whether 
some of its members live on and assume the aspect of the 
obtusifrons generation ; according to my knowledge of the cycle 
in the Danish lakes, I feel inclined to consider the first view as 
the correct one. 
Copepoda. 
Diaptomus minutus, Lilljeb. 
The Diaptomus species of the Thingvallavatn is the easily 
recognisable D. minutus (Lilljeborg). It is described by Lilljeborg 
from Greenland and Newfoundland ; it is mentioned by Marsh 
(1893, p. 199) from Green lake, North America. In a subsequent 
paper (1897, p. 8) Marsh describes it as the commonest of all 
Diaptomidae appearing in samples collected in the great American 
lakes. 
Richard and De Gueme (1889, p. 632) states that it has been 
found in Greenland near Tasersuak. The species of the Thing- 
vallavatn has already some time ago been determined as D. minutus 
by the same authors. 
On 14th July D. minutus occurs in enormous numbers, but only 
as young ones. On 31st July I found many males with spermato- 
phores within their bodies ; the abdomen of the females is quite 
straight and the oviducts hardly noticeable ; some females have 2 to 3 
eggs. From 14th August till 15th September the sexual period is at 
its max. Males and females are nearly equal in number ; the males 
all have spermatophores in their bodies, and the females often carry 
a cluster of 4 to 5. The egg-sacks never contain more than 4 
