LAND AND FRESH WATER MOLLUSCA OF BUTE. I73 



"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 Planorhis and LimncBa 

 get mto 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 ivith 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 Kothesay 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 



^ 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 Helicidfe 

 -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 sixle was not examined so thoroughly as the 

 other. I feel assured, however, that the chief reason 

 was the absence of molluscan species, due perhaps 

 to unsuitability of habitat. The finding of so many 



