376 The Upper Elf Loch, Braids. [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- 

 narius 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 ftiscata and Graptoleberis 

 testudinarius. Daphnia pulex 1 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 Schoedleri, 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. 





