INTRODUCTION. 39 



Limn&us glaber^ Amphipeplea glutinosa, would have 

 been inserted in the list of local species. The latter, 

 though found in Sweden and France, is not recorded 

 as a German species by PfeiiFer. Though very local 

 where found, these and other species similarly circum- 

 stanced have been found, dispersedly, in very different 

 parts of the islands. 



Besides fewer species being found in the northern 

 parts of our island than in the south, the specimens 

 of the species are said to be much more rare. This is 

 probably partly owing to the rigours of the climate, 

 and partly to the country consisting of the older geo- 

 logical formations, which are less favourable to the 

 support of these animals than the calcareous rock, 

 which appears to be their favourite habitation. 



M. D'Orbigny, who has paid great attention to the 

 distribution of these animals, especially in South Ame- 

 rica, says, the terrestrial Pulmonobranchiata are much 

 more abundant in the warmer regions of the different 

 quarters of the globe than in the more temperate parts, 

 while the aquatic species are more abundant in the 

 latter than in the former. 



He observes that the terrestrial species gradually 

 diminish in number as we proceed from the warmer 

 regions towards the pole ; and as we ascend from the 

 plains to the tops of mountains. Out of the 156 spe- 

 cies which he found in South America, 137 were found 

 between the llth and 28th : 28 between the 28th and 

 34th; and only 13 between the 34th and 45th degrees 

 of south latitude; and 126 species were found under 

 5000 feet, while only 4 were found above 5000 feet 

 and below 11,000 feet, and 6 at more than 11,000 

 feet, above the level of the sea. 



