MINERALS AND GEOLOGY OF CANADA. 



121 



Pig. 123. 



Kg. 124. 



Fig. 125. 



represent several of our more characteristic Canadian examples. 

 Figure 121 is the Ophileta (formerly Maclurea,) compacta of the 

 Calciferous-sand group (Lower Silurian.) Pig. 122 represents 

 Murchisonia gracilis, (a, shewing internal cast) ; and fig. 123 exhibits 

 a cast of Murchisonia sul-fusiformis of the Trenton and Hudson 

 Biver Groups. Pleurotomaria (or Trochonema) mnhilicatula, a com- 

 mon Trenton fossil, is shewn in fig. 124 ; and a cast of EuonvpJialus 

 rotundm (?), a Devonian form, in figure 125. 



The Pulmonifera, in place of branchiae, possess a simple form of 

 lung-structure by which they breathe air directly from the atmos- 

 phere. Some, as the snails, are terrestrial ; others inhabit ponds, 

 streams, and fresh-water lakes. AD are vegetable-feeders ; and 

 the shell, in those forms which secrete one, is more or less light and 

 thin. Our only fossilized examples, comprising existing species of 

 Selix, Limnea, Flanorhis, &c., occur in the higher Drift or Post- 

 Tertiary deposits of Western Canada. These will be referred to, 

 more particularly, in Paet V. 



The concluding part of this division of our subject, embracing the 

 Cephalopods, &c., will be given in a succeeding Number of the 

 Journal. 



