54 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



i'20 25 30 35 40 45 50 55 

 2 VALVE HEIGHT (MM) 



60 655 20 25 



30 35 40 45 50 55 . 60 65 

 VALVE HEIGHT (MM) 



20 



25 30 35 40 45 50 55 60 65 

 VALVE HEIGHT(MM) 



20 25 30 35 40 45 50 55 60 65 

 VALVE HEIGHT(MM) 



30 35 40 45 50 

 VALVE LENGTH (MM) 



Fig. 17. — Ontogenetic development of Lopha bellaplicata bellaplicata (Shumard). 

 A, Relationship between number of denticles in 5 mm. length (measured along 

 margin) and valve height, showing decrease in density with age, and with 

 increase in size. B, Relationship between the height of the valve and the extent 

 of the denticulate portion of the margin, measured in terms of height, showing 

 increase in extent of denticles with age and size. C, Relationship between length 

 of hinge line and valve length, showing increase in size of hinge line relative to 

 lateral expansion with age and size. All lines fitted visually. Approximate 

 boundaries between ontogenetic stages marked by dashed lines. E = Ephebic ; 

 T = Ephebic-Gerontic transition ; G = Gerontic. 



