NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 



65 



Table 5. — Summary of measurements for Lopha bellaplicata 

 novamexicana — continued 



Character Valve 

 Number of plicae in 20 mm. length 

 at 20 mm. height 3 



Width of median plica 20 mm. below 

 beak L 



Percent increase in plicae by bifurca- ^ j 



^°" |r 



Width of posterior auricular sulcus 



20 mm. below beak L 



Inclination of beak, umbo (67 left 



valves, 8 right valves) : ^^ 



Percent opisthogyre \^ 



I is. 



Percent orthogyre ) 



Percent prosogyre ) 



/ 



Length of hinge line (LHL) ) 



/ 



Ratio, LHL:L \^ 



I 

 Number of denticles in 5 mm. length . ) 



I 

 Maximum diameter of muscle scar 



(MDS) L 



Ratio, MDS : H L 



Ratio, area of scar : area of valve. . . L 



rounded. Posterior margin straight to gently curved except in valves 

 with prominent posterior auricle, where concave notch developed in 

 outline at intersection with posterior auricular sulcus. Dorsolateral 

 margins straight to slightly curved; dorsolateral comers narrowly 

 rounded over auricles. Anterodorsal margin steeply to moderately 

 inclined ; inclination least in presence of auricle. Posterodorsal mar- 

 gin longest, moderately inclined with or without auricle. 



Left valve moderately to highly convex (pi. 8, figs. 1-3) ; high point 

 dorsocentral, just anterior to midline, on median plica. Anterior and 

 dorsal flanks steeply sloping; ventral, posteroventral, posterodorsal 

 flanks moderately sloping ; posterior flank slopes steeply into auricular 

 sulcus, becomes flat beyond this. Right valve flat to slightly concave 

 dorsally and centrally, slightly convex ventrally, ventrolaterally, rarely 



