1916 



Du Bois; on Brachiopods 



183 



By working out the relationships between the variation of individ- 

 uals and the physical conditions of the habitat in this manner, the paleon- 

 tologist may be able to throw much light on the conditions under which 

 some of the fossil forms lived. The writer has in progress such a study 

 of the variation of the Devonian brachiopod, Stropheodonta demissa (Con- 

 rad), as shown in the Devonian (Hamilton) of the northwest province, 

 which promises very definite results. 



PLATE 32 



View of shells of Terebratalia obsoleta Sowerby, showing variation 

 resulting from difference in habitat, injury, etc. 



2. Normal shaped specimens from quiet water. 



Specimen showing some effect of rough water. 



Typical tide-line specimen from Turn Island, 



Effect of local injury. The growth lines have "a puckered 



Figs. 1 



Fig. 3. 



Fig. 4. 



Fig. 5. 

 appearance." 



Fig. 6. Specimen with such an injury healed. The growth lines 

 have gradually resumed their regularity. 



Figs. 7, 8. Effect of injury to one side of the mantle. 



