BRITISH NON-MARINE MOLLUSC A. 



43 



phanerogamic vegetation and Filices, and in which work a series 

 of vertical or ascending zones will be found described for every 

 latitude in the British Isles. In the * Entomologist ' for January, 

 1894, I also proposed and tabulated a similar series for the pur- 

 pose of studying the perpendicular distribution of the British 

 Lepidoptera, based principally on the statistics given in the 

 * Meteorological Atlas of the British Isles,' published by the 

 Council of the Koyal Meteorological Society,' at the same time 

 giving their equivalents in the principal mountain ranges of 

 Central and Southern Europe, as well as in Scandinavia, for 

 purposes of comparison. These would suffice equally well for 

 the Mollusca. 



The Bathymetrical Distribution of the British non-Marine 

 Fauna, particularly the Mollusca, opens up another important 

 field for investigation and inquiry which has hitherto been very 

 badly neglected, if not, indeed, wholly ignored. It is easy to 

 understand that the practical study of the depths to which the 

 Marine Mollusca descend is beyond the power of most in- 

 dividual students, by reason of the elaborate preparations neces- 

 sary in conducting dredging operations and the expense entailed 

 thereby. But its application to the freshwater denizens of our 

 lakes and extensive expanses of water prevailing more par- 

 ticularly in the northern parts of these islands, would afford 

 much less difficulty of attainment, and the results accruing 

 therefrom would no doubt be of inestimable service to zoology, 

 as has recently been the case in the bathymetrical investigation 

 of the fauna of the Alpine tarns in Switzerland. 



It has been my good fortune, from a conchological point of 

 view, to be located during the past season on the plateau of the 

 Cotteswolds in Gloucestershire at an altitude of close upon 

 1000 ft. above the sea-level. The range of elevation is not great 

 from the point of view of the study of the vertical distribution of 

 the Mollusca, only three points in the whole chain — which 

 extends from Bath in the south-west to near Stratford-on-Avon 

 in the north-east — just exceeding 1000 ft. above the sea-level, the 

 average elevation of most of the hills being between 500 ft. and 

 900 ft. The entire district therefore comes within Dr. H. C. 

 Watson's two lowest climatal or phytogeographical zones, 

 namely, his lower agrarian and mid-agrarian zones. The 



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