of the Fishery Board for Scotland. 



141 



The total number of species of Crustacea obtained in the hand-net 

 gatherings was sixty-one, and of the mollusoa nine. The formula shows 

 the number of species belonging to each of the groups of Crustacea — 

 Amphipoda (1), Isopoda (2), Copepoda (3), Ostracoda (4), and Cladocera 

 (5)— obtained in the different gatherings, and also the total number in each 

 gathering. (The figures are now in the formula in place of the names.) 



Date. 



August 20. 



November 23. 



March 22. 



June 21. 



Numbers of the Groups, 



Number of Species in 

 each Group, 



Total Number in each 

 Gathering, 



I, 2, 3, 4, 5. 



1, 2, 3, 4, 5. 



1, 2, 3, 4, 5. 



1, 2, 3, 4, 5. 



1, 0, 8, 3, 12. 



1, 0, 11, 5, 12. 



1, 1, 7, 7, 6. 



0, 1, 12, 11,13. 



23. 



29. 



22. 



26. 



Moreover, the total number of species belonging to each of the five 

 groups obtained in all the four gatherings is, as shown by the Table : — 

 Amphipoda, one species ; Isopoda, one species ; Copepoda, nineteen 

 species ; Ostracoda, sixteen species ; and Cladocera, twenty-four v 'species. 

 It will be observed that a few somewhat rare forms were obtained in 

 the Loch Lomond gatherings, the following of which may be mentioned 

 here : — Cyclops dybowskyii, Lande (this has not been found in any other 

 loch in Scotland) ; Ganthocamptus sclwneilii, Mrazek (so far, the only 

 localities for this species in Britain are Loch Leven, Loch Lomond, and 

 one or perhaps two other Scottish lochs) ; Monospilus dispar, G. 0. 

 Sars (this species has been observed in only a few places in Scotland). 



It is probable that some of these shore forms, as well as of those that 

 live in the more open water, are affected by the changes incidental to the 

 different seasons ; but to obtain satisfactory evidence of this would require 

 a lengthened investigation, because the influences that react on these 

 shore forms are more complex. They are, for example, more likely to 

 be subjected to greater extremes of heat and cold. Moreover, droughts 

 may occur in spring or summer or autumn that will have a much greater 

 influence on these organisms than upon those that live out in the open 

 water — at least, if the water be of moderate depth. The effect of floods 

 will also have a more perceptible influence on the shore fauna, and these 

 are phenomena that are not necessarily incidental to any particular 

 season. It is probable that the curious changes that are sometimes 

 observed in the distribution of the non-pelagic entomostraca may be due 

 to accidental causes such as these, and not to the usual seasonal changes. 



During two of my visits advantage was taken of the opportunity to 

 examine a small loch near Loch Lomond, called the Dhu Lochan. 

 The Dhu Lochan is distant about two miles from Rowardennan, and near 

 the road leading south to Balmaha. A small stream issues from its north 

 end, and, after a somewhat circuitous course, falls into Loch Lomond. 

 This , little loch was examined with the hand-net, and a considerable 

 number of interesting Entomostraca were found in it. A number of them 

 were similar to those found in Loch Lomond, but the following compara- 

 tively rare species are additional to those recorded for that loch : — Cyclops 

 nanus, G. O. Sars ; Cyclops affinis, G. O. Sars ; Scaplwleberis mucronata 

 (Midler) ; Streblocercus minutus, G. O. Sars ; Drepanotlirix, dentata 

 (Euren) ; Acantholeberis curvirostris (Miiller) ; Ilyocryptus sordidus 

 (Lievin) ; Alonella nana (Baird) ; Peracantha truncata (Miiller). 



