NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 



15 



LEFT VALVE 



L.BELLAPLICATA- 

 BELLAPLICATA 



y 





\ 



.i & 





A 





L. LUGUBRIS 



L. BELLAPLICATA 

 NOVAMEXICANA 



^0 5'5 go" 



"^ 



30 35 40 45 

 HEIGHT (MM) 



10 



30- 

 25- 



10 



5^ 



LEFT VALVE 

 L. BELLAPLICATA NOVAMEXICANA- 





rA NOVAMEXICANA Z^"*^ ^ . A/ 



L. BELLAPLICATA 



BELLAPLICATA 



15 10 15 20 25 30 35 40 45 50 55 60 65 70 



HEIGHT (MM) 



Fig. 4. — Evolution in the Lopha lugubris group. A, Scattergram showing 

 relationship between valve height and the distance between the beak and high 

 point of the left valve, measured parallel to height. Note ventral shift of the 

 high point in progressively younger forms. Arrow in lower left-hand corner 

 denotes direction of ventral migration of high point as illustrated by hypothetical 

 regression lines fitted visually to plots of end members of group. B, Scattergram 

 showing relationship between height and width of left valves. Note slight 

 decrease in relative convexity of left valve in progressively younger forms. 

 Arrow in lower left-hand corner denotes direction of decreasing convexity as 

 illustrated by hypothetical regression lines fitted visually to plots of end members 

 of lineage. 



