246 THE SCOTTISH NATURALIST 



GENERAL NOTES ON HABITATS AND OCCUR- 

 RENCES OF LAND AND FRESH -WATER 

 MOLLUSCA IN THE NORTH OF SCOTLAND. 



By Fred Booth. 



[This is the fifth of the series of notes on investigation of the northern 

 range of mollusca in Scotland, undertaken by aid of a Government 

 grant. W. D. R.] 



A STRIKING feature in regard to local distribution in the 

 parts of the north of Scotland which I visited in August 1910 

 is the character of the habitats ; and these habitats define 

 strict areas for mollusca, with large intervening areas which 

 to all intents and purposes appear to be devoid of molluscan 

 life. 



Certain conditions and certain associations of plant-life 

 appeared to be necessary to constitute a habitat of the 

 desired nature to produce shell-life in any degree of 

 commonness. Though to all appearance many other situa- 

 tions appeared suitable, the most diligent search of them 

 failed to produce a single specimen. 



This experience is totally different from what is met 

 with in Yorkshire and Lancashire, where in most valleys 

 there is a continuity of shell-life, though the habitats vary 

 very considerably. 



In the disintegration or falling away of the rocks in 

 northern Scotland, the particles do not appear to dissolve 

 away into fine particles, like our Yorkshire rocks, whether 

 limestone or grit, which settle down amongst the vegetation 

 and quickly assume a soily nature, but are left in a gritty or 

 rough granular state, which to all appearance is detrimental 

 to crawling mollusca. 



The only habitats which appeared likely to yield 

 specimens were those where a certain amount of moisture 

 had given rise to rank vegetation, which from year to year 

 in falling away had left a substratum of decaying matter 

 consisting of dead leaves, mosses, etc. This kind of habitat 





