ZOOLOGY 



MOLLUSCS 



From a conchological point of view the county of Derbyshire may 

 be conveniently divided into four districts. 



1. The Peak, or Grit and Heather District, consisting of the north- 

 west corner cut off by a line from Hathersage through Castleton, 

 Chapel-en-le-Frith to Whaley Bridge. This portion of the county is 

 particularly barren of molluscs owing to the absence of lime for the 

 formation of the shells. 



2. The Limestone District, of oblong form, with Hathersage, Chapel- 

 en-le-Frith, Ashbourne and Derby at the corners. This district is very 

 rich in land molluscs, but the absence of ponds other than farmyard 

 duck-ponds accounts for the absence of freshwater species. 



3. The Triassic Marls and Sandstone District which comprises the 

 south of the county is, like the Millstone Grit district though to a less 

 extent, poor in terrestrial species. 



Aquatic species, on the other hand, are well represented owing to 

 the number of canals traversing this portion of the country. 



The rivers of Derbyshire are particularly unfruitful, probably on 

 account of the scanty weed supply, the swiftness of the currents and the 

 coldness of the water when the snow melts on the hills, as well as the 

 presence of lead in solution. 



4. The Coal Measure District. The remaining (eastern) division of 

 the county may be termed the Coal Measure district, and is superficially 

 composed of shale and marl and new red sandstone. It is the most 

 unprofitable collecting ground of all the county, being almost destitute 

 of land and freshwater species alike. 



Of the 139 species known to occur in the British Islands, 99 are 

 met with in Derbyshire, and it is not likely that more than one or two 

 others will ever be added to the list. The following have been recorded 

 but their identification is too doubtful to admit of their inclusion : 

 Amalia gagates, Vitrea lucida, Hygromia granulata, and Amphipeplea 

 glutinosa. Acanthinula lamelleta and Vertigo moulinsiana are included 

 on the authority of the Records of the Conchological Society, though 

 further confirmation would be welcomed. 



The assemblage is of the average north British type. 



