INTRODUCTION. 



THE District of which the Mollusca are described in the 

 following pages, constitutes the north-eastern portion of 

 the middle Division of Scotland. Besides the extensive 

 County of Aberdeen, it includes the smaller Counties of 

 Kincardine and Banff, the former on its southern, the 

 latter on its north-western side. Bounded toward the east 

 and north by the German Ocean, it stretches inland 

 toward the central ridges of the Grampians, in which 

 are some of the highest summits in Britain, giving rise 

 to the sources of the Dee and the Don, as well as tribu- 

 taries of the Spey. The latter river bounds the district 

 to the north-westward, while the southern boundary runs 

 eastward from the western sources of the Dee to Mount 

 Battock, and thence to the neighbourhood of Bervie. 

 The upper part of the district is mountainous, with 

 narrow valleys, partially wooded ; but the land declines 

 eastward and northward, although still hilly, and toward 

 the coast becomes comparatively level. The rocks are 



