98 



Mr. M. C. March on the 



Arcidae wliich grow slowly and have a thin test. Here tlie 

 transition between dysodont and taxodont teeth is clearly 

 seen. The Monomyarians develop rudimentary dysodont 



Fig. 5. 



PJL 



AE 



Fecten varius, showing the first dysodont teeth. (After Bernard.) 

 Fig. 6. 



Plicatula ramom, 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 



