56 



Proceedings of the Royal Physical Society. 



to show the relative abundance of each species rather more 

 accurately than can be done by the usual mode of using 

 variants of common (c, cc, ccc) and rare (r, rr, rrr), as is 

 often done. To this end I have divided Scotland into ten 

 convenient districts, and taken the loch as a unit. The 

 figures in the columns, then, under each district, and opposite 

 each species, indicate the number of lochs in that district 

 in which that species was found. When exact data are 

 not available, the following signs are employed : — * indicat- 

 ing that a species has been noted by Dr Scott, f that it has 

 been observed by the Lake Survey, although the number of 

 lochs cannot be given. 



Distribution of some Crustacea and Desmids in the 

 Scottish Lakes. 



