of the Fishery Board for Scotland. 271 



imperial acres was reduced to 3,238 acres.* Its present area is now some- 

 what greater, being about 3,406 acres, f 



As so much interest centres round this famous loch, it was considered 

 desirable that its invertebrate fauna should be carefully investigated, in 

 order to ascertain if the marked superiority of the trout was in any way 

 owing to a difference in the kind of organisms thatl form their food 

 supply. 



I made an examination of the loch during the month of June last 

 (1890) by means of dredge and tow-net, worked from a rowing-boat, 

 kindly placed at my service by Mr Hall, the manager of the Fishery, and 

 also by hand-net from the shore. Unfortunately/the weather was rather 

 stormy at the time, and interfered somewhat with the satisfactory carrying 

 out of the investigations ; nevertheless, the results of the examination of 

 the loch were of considerable interest. The fauna was found to be abund- 

 ant and varied — Mollusca, Arthropoda, Annelida, and Protozoa being 

 more or less common all over the loch. The present report deals chiefly 

 with the first two classes named, because they are in several respects the 

 more important of the invertebrata ; the others, while]£tliey also are 

 referred to here, may be more fully worked out in a future report. 



I propose to refer to the various classes of orgauismsjn the order in 

 which they are arranged above. 



Mollusca. 



Mollusca were common and generally distributed, except at that part of 

 the loch called the ' Shallows,' the bottom of which consists of little else 

 than fine sand, and is therefore not so suitable as a habitat for these 

 organisms as where the bottom consists of mud or vegetable debris. Four- 

 teen species of Mollusca were obtained, comprising five of Lamellibranchs, 

 and nine of Gasteropods. The more common forms were Sphcerium 

 corneum, Valvata piscinalis, and Planorbis contortus. The swan mussel 

 (Anodonta cygncea) appeared also to be frequent, — that is, if the number of 

 dead shells observed atTseveral places along the shore can be relied on as 

 evidence of the presence of this shell-fish. I was only able, however, to 

 obtain living, one adult, and a few young specimens ; the latter were 

 found burrowing in the sand in the shallow water at the north-east side of 

 the loch. The following is a list of the species of Mollusca obtained : — 



MOLLUSCA. 



1. Lamellibrachiata. 



Sphcerium corneum (Linns). Generally distributed, common. 

 Pisidium fontinale (Draparnaud). Generally distributed, common. 



,, puillicm (Gmelin). Generally distributed, frequent. 



,, nitidum (Jenyns). Generally distributed, frequent. 

 Anodonta cygncea (Linne).* {Frequent (?), 1, adult and several young living. 



2. Gastropoda. 



Valvata piscinalis (Miiller). Generally distributed, common. 



,, cristata, Miiller. Generally distributed, but scarce. 

 Planorbis albus, Miiller. Generally distributed, rather scarce. 



,, nautileus (Linne). West end of the loch, but not common. 



,, contortus (Linne). "^Generally^distributed, common. 



* I understand the mill-owners have still the power of diminishing the lake by 2^ 

 feet, a total of 7 feet lower than it was in the beginning of the century, 

 t Fifth Annual Report, Fishery Board for Scotland, p. 367, 1887. 



