of the Fishery Board for Scotland. 285 



water, calculated from the bench mark on Kenmore Bridge, is found to be 

 346 feet above the sea. The general outline of the loch somewhat 

 resembles the letter S in form but with the ends only slightly curved. 

 The lower portion of the letter is represented by the part from Killin to 

 Ardionaig and extends E. 25° N". about 5|- miles, the middle portion is 

 represented by the part from Ardionaig to Fernan and extends 1ST. 30° E. 

 about 5| miles, and the upper portion is represented by the part extending 

 from Fernan to Kenmore, and which lies in the same direction as the 

 west end, viz., — E. 25° N. The length of this portio is about 3J miles. 

 ,The deepest part of the loch is opposite Skiag, or a litue over 5 miles in a 

 * bee line ' from Kenmore ; the depth here is 85 fathoms or 520 feet. 

 From this deep part of the loch the bottom rises gradually but more or 

 less irregularly towards each end. When the loch is standing at its 

 summer level the western margin is often covered with thin patches of 

 bright red sand which, on examination, is found to be composed almost 

 entirely of minute fragments of garnets ; numerous fragments of 

 garnetiferous schist may also be obtained scattered about the shore at the 

 east end of the loch. 



Invertebrate Fauna of Loch Tat. 



The Loch was examined by means of a tow-net worked from a rowing 

 boat kindly placed at my disposal by a friend in Kenmore. No examina- 

 tion was made of the bottom of the Loch except where the water was 

 shallow, that is between the steam-boat pier and the ' Minister's Island ' 

 on the south side, and from Aidan's Isle eastward on the. north side. 

 Pelagic Crustacea were scarce in all the surface and under-surface gather- 

 ings, but they included one or two forms of interest, such as the curious 

 Bytlwtrephes and the beautiful Leptodora. On the other hand, the 

 material collected by dragging the tow-net through and among the bottom 

 vegetation found growing in some of the shallower parts and especially 

 in the vicinity of the ' Minister's Island ' proved to be rich in micro- 

 organisms ; over twenty species of Crustacea were obtained in this way. 

 Several species of Mollusca, Coleoptera, Arachnida, the larvae of dragon- 

 flies and other insects, Ehizopoda, Rotifera, &c. were also observed in 

 the same material. In the following lists I propose to give a record only 

 of the species of Mollusca and Crustacea obtained. 



THE MOLLUSCA. 



Comparatively few species of Mollusca were observed in Loch Tay, 

 and this paucity of molluscan species corresponds with what I have 

 observed in the investigation of other deep fresh-water Lochs; the 

 conditions physical or otherwise of such lochs do not seem to favour the 

 development of the Mollusca. 



1. Lamellibranchiata. 



Pisidium pusillum (Gmelin). Frequent, 



„ fontinale (Drap$), Scarce, 



2. Gasteropoda. 



,. ,., .. . Frequent, ) but generally of 



Valvata piscinahs (Muller). , BmSL \\ s i ze 



U 



