450 THE CANADIAN NATURALIST. [Yol. IS,. 



ordinary gill-bearing Gasteropods, is the one which has been 

 traced farthest back, and includes the Paleozoic species. It is 

 further remarkable that a very great gap exists in the geological 

 history of this family. No species are known between the Car- 

 boniferous and the early Tertiary, though in the intervening 

 formations there are many fresh-water and estuarine deposits in 

 which such remains might be expected to occur. There is per- 

 haps no reason to doubt the continuance of the HelicidiB through 

 this long portion of geological time, though it is probable that 

 during the interval the family did not increase much in the 

 number of its species, more especially as it seems certain that it 

 has its culmination in the modern period, when it is represented 

 by very many and large species, which are dispersed over nearly 

 iill parts of our continents. 



The mode of occurrence of the Paleozoic Pulmonifera in the 

 few localities where they have been found is characteristic. 

 The earliest known species. Pupa vestuta, was found by Sir 

 Charles Lyell and the writer, in the material filling the once 

 hollow stem of a Sigillaria at the South Joggins in Nova Scotia, 

 and many additional specimens have subsequently been obtained 

 from similar repositories in the same locality, where they are 

 associated with bones of Batrachians and remains of Millipedes. 

 Other specimens, and also the species Zonites prisons, have been 

 found in a thin, shaly layer, containing debris of plants and 

 trusts of Cyprids, and which was probably deposited at the out- 

 let of a small stream flowing through the coal-formation forest. 

 The two species found in Illinois occur, according to Bradley, in 

 an underclay or fossil soil which may have been the bed of a 

 pond or estuary, and subsequently became a forest sub-soil. The 

 Erian species occurs in shales charged with remains of land plants 

 and w^hich must consequently have received abundant drainage 

 from neighboring land. It is only in such deposits that remains 

 of true land-snails can be expected to occur; though, had fresh- 

 water or brackish water Pulmonates abounded in Carboniferous 

 ao-e, their remains should have occurred in those bituminous 

 and calcareo-bituminous shales which contain such vast quan- 

 tities of debris of cyprids, lamellibranchs and fishes of the period, 

 mixed w'ith fossil plants. 



With reference to their affinities, the Paleozoic land snails 

 present no very remarkable peculiarity except their close resem- 

 blance to some modern forms. Of the known species, four be- 



