THE OLDEST AIR-BREATHERS 293 



been sufficiently dry to allow several feet of the imbedded 

 hollow trunks to be free from water. In the highest of the 

 three horizons the shells occurred in an erect tree, but without 

 any other fossils, and they had apparently been washed in 

 along with a greyish mud.^ 



If we exclude the alleged Palceorbis referred to below, all 

 the Palaeozoic Pulmonifera hitherto found are American. 

 Since, however, in the Carboniferous age, Batrachians, Arach- 

 nidans. Insects and Millipedes occur on both continents, it is 

 not unlikely that ere long European species of land snails will 

 be announced The species hitherto found in Eastern 

 America are in every way strangely isolated. In the plant 

 beds of St. John, about 9,000 feet in thickness, and in the 

 coal formation of the South Joggins, more than. 7,000 feet in 

 thickness, no other Gasteropods occur, nor, I believe, do any 

 occur in the beds holding land snails in Illinois. Nor, as 

 already stated, are any of the aquatic Pulmonifera known in 

 the Palaeozoic. Thus, in so far as at present known, these 

 Palaeozoic snails are separated not only from any predecessors, 

 if there were any, or successors, but from any contemporary 

 animals allied to them. 



It is probable that the land snails of the Erian and Carboni- 

 ferous were neither numerous nor important members of the 

 faunae of those periods. Had other species existed in any 

 considerable numbers, there is no reason why they should not 

 have been found in the erect trees, or in those shales which 

 contain land plants. More especially would the discovery of 

 any larger species, had they existed, been likely to have 

 occurred. Further, what we know of the vegetation of the 

 Palaeozoic period would lead us to infer that it did not abound 



1 The discovery of the shells in this tree was made by Albert I. Hill, 

 C.E. The tree is in Group XXVI. of Division 4 of my Joggins section. 

 The original reptiliferous trees are in Group XV., and the lowest bed in 

 Group VIII. 



