200 LAND AND ERESH-WATER MOLLUSKS. 
rounded for tlie most part by bog. Tbe water, 
impregnated by vegetable matter, is almost of a 
coffee colour, but generally clear, and the whole 
region has a wild and desolate aspect, strangely 
contrasting with the charming scenery we have 
just left. During the first quarter of an hour, I 
searched diligently on the leaves and stalks of 
the water-plants growing in the lake, and scooped 
up quantities of mud, which I carefully examined, 
but not a shell could I find. Water, rock, and 
mollusk were nearly of one colour; but by 
kneeling down beside the tarn, and putting 
my face almost close to the surface, I was able to 
see to some distance into the water. After 
gazing steadily for a few minutes, I thought I 
discovered two Limnceas crawling up the side of 
the rock, and a little careful manipulation with 
the scoop soon put me in possession of the 
prize. I spent about two hours at the lake, and 
took eleven specimens of the Limncea in addition 
to the first, which the guide had broken, and 
in every instance the mollusk was either crawl¬ 
ing on rocks or free; never attached to aquatic 
plants, or found in the mud. Had the day been 
bright and calm, I dare say I should have col¬ 
lected a greater number; but where the breeze 
rippled the surface of the water, it was impossible 
to see anything accurately, even at the depth of 
a few inches, unless it differed much from the 
