376 The Upper Elf Loch, Brazds. [Sess. 
surface of the water, to allow the hand-net to be introduced 
and worked underneath it, the ice at the time being fully 
half an inch in thickness. These five species may therefore 
safely be regarded as permanent inhabitants of the loch. 
Moreover, it will be observed that several other species have 
been obtained so frequently that they also may be expected 
to occur more or less constantly all the year round, and their 
absence from some of the gatherings may in some instances 
at least be accounted for by their being overlooked. But, on 
the other hand, though the non-occurrence of some species 
may be accounted for in this way, the intermittent appearance 
of others seems to require a different explanation. There 
are, for example, a few species, such as Cypris fuscata and 
Graptoleberis testudinarius, that appear to have a more or less 
regular seasonal increase and decrease. Cypris fuscata has 
been observed in spring and early summer, sometimes in 
considerable abundance: it was obtained in March and October 
1896, in March and May 1897, and in February and April - 
1898, but we failed to observe it on the 9th of May and 
the 18th of July 1896, as well as on our visits in June, 
July, September, and November 1897. Graptoleberis testudi- 
narvus differs somewhat from Cypris fuscata in its seasonal 
distribution. It was obtained in May and July 1896, and 
in July and September 1897, while no trace of it has been 
observed during the colder months. Another example of 
difference in seasonal distribution may be referred to, but in 
this case the difference is between species much more closely 
related to each other than Cypris fuscata and Graptoleberis- 
testudinartus. Daphnia pulex’ and Simocephalus vetulus, which 
are both found in the Elf Loch, are so nearly related that they 
were formerly considered to belong to the same genus. In 
the gathering collected on the 9th of May 1896, Daphnia 
pulex was common, but Simocephalus vetulus was rare. In 
the gathering collected on October 17th of the same year, 
Daphnia is again predominant, and is recorded in our notes 
1 The Daphnia pulex found in the Upper Elf Loch is usually furnished with a 
moderately long and slightly curved posterior spine: this form has been described 
as a distinct species, under the name of Daphnia Schedleri, but it is now re- 
garded as merely a variety of Daphnia pulex. What is considered as the typical 
form of D. pulex has no elongate posterior spine, but the test terminates in an 
acute point. Like other Daphnias, it is extremely variable. 
