98 



Mr. M. 0. Marcli on the 



Arcidffi wliicli grow slowly and have a thin test. Here the 

 transition between dysodont and'taxodont teeth is clearly 

 The Monomyarians develop rudimentary dysodont 



seen. 



Fie:. 5. 



PIT 



AH 



Tecten varius, showing the first dysodont teeth. (Alter Bernard. 

 Fio-. 6. 



Plicatula rmnosa, showing the development of I, II, and III. 

 (After Bernard.) 



teeth, which show extraordinary variation. Bernard con- 

 cludes from these facts that they are degenerate. 



An important fact brought out by Bernard is the order of 



