173 LAND AND FRESH WATER MOLLUSCA OF BUTE. 
be seen, although all the fresh-water tanks were 
supplied from the same source, viz., Loch Ascog. It 
would thus appear that the pike were inclined to 
look after larger “game” than tiny molluscs. It 
may be asked: How did the Planorbis and Limnea 
get into the tanks? The reason is simple enough; 
the water from Loch Fad was not filtered, and conse- 
quently numbers of Mollusca as well as Entomostraca 
were occasionally brought down along with the 
water into the tanks. 
Loch Fad. 
This loch is artificially divided into two parts by 
an embankment formed across it opposite the farm 
of Lochly. A road is carried along the top of the 
embankment, which is very convenient for persons 
wishing to cross to the other side. The part next 
to Rothesay is called the “Kirk Dam,” and the 
other is known as Loch Fad proper. The extreme 
length of the loch, including both parts, is about 
24 miles; while the breadth, which is somewhat 
variable, is barely a quarter of a mile at the . 
embankment. 
Loch Fad occupies part of a natural hollow or 
valley stretching in a north-easterly and south- 
westerly direction. The south-east side of the loch 
is formed of carboniferous rocks—sandstone, shale, 
and trap;—the north-west side is of grey schistose 
rocks, passing in some places into blue slate. Along 
the south-east side, from the embankment south- 
westward, I found a considerable number of Helicidee 
—20 species at least—including 4 species of Vertigo. 
As a matter of fact, I found here a greater variety 
of Mollusca than in any of the other places ex- 
amined. I did not find the north-west shore so 
productive, but one reason for this might be that 
that side was not examined so thoroughly as the 
other. Iifeel assured, however, that the chief reason 
was the absence of molluscan species, due perhaps 
to unsuitability of habitat. The finding of so many 
