NO. 6 OYSTERS OF THE LOPHA LUGUBRIS GROUP — KAUFFMAN 



59 



irregularly curved, without anterior auricle. Ventral margin moder- 

 ately to narrowly rounded, regular to irregular. Posterior margin with 

 irregular outline, slightly concave (outward) dorsally, moderately to 



Table 3. — Summary of measurements on left valves of Lopha bellaplicata 

 bellaplicata var. A 



No. of 



Character specimens Range Average 



Height (H) 21 15.4-38.4 mm. 23.4 mm. 



Length (L) 22 10.1-29 mm. 17.0 mm. 



Ratio, L:H 17 0.56:1-1.20:1 0.73:1 



Width (W) 23 3.0-12.9 mm. 7.7 mm. 



Area, inscribing rectangle of valve 



(A) 20 179.6-1128.1 mm.== 432.9 mm." 



Length ; beak to posterior margin 



(LBP) 22 3.9-14.4 mm. 9.4 mm. 



Ratio, LBPrL 21 0.39:1-0.71:1 0.53:1 



Angle of incHnation (i) 20 67-101° 82.3° 



Height of attachment scar (HATS) : 



Maximum vertical diameter 20 2.6-21.9 mm. 9.8 mm. 



In plane of commissure 20 1.4-21.9 mm. 8.4 mm. 



Length of attachment scar (LATS). 20 2.3-17.2 mm. 9.5 mm. 

 Area, inscribing rectangle of attach- 

 ment scar (HATS X LATS) .... 20 6-354.8 mm." 110.6 mm." 

 Height, smooth young stage (HSS), 



dorsal part of valve 22 2.3-23.4 mm. 9.98 mm. 



Height, plicate portion of valve 20 4.9-26.5 mm. 13.6 mm. 



Ratio, H : HSS 20 0.108 : 1-0.777 : 1 0.432 : 1 



Number of plicae at first appearance. 22 4-12 8 



Number of plicae at 10 mm. height. . 14 4-12 8.5 



Number of plicae at 20 mm. height. . . 16 5-12 9.6 



Total number of plicae 22 4-14 9.3 



Number of plicae in 10 mm. distance 



(length) 10 mm. below beak 13 3-6.75 4.8 



Width of median plica at 10 mm. 



height 21 0.8-2.6 mm. 1.7 mm. 



Percentage of plicate valves with 



bifurcating plicae 23 78.3% 



Percentage increase in number of 



plicae by bifurcation 18 9.1-41.7% 17.9% 



Curvature of beaks and umbones : . . . 21 



Opisthogyre 81% 



Orthogyre 9.5% 



Prosogyre 9.5% 



slightly convex ventrally (pi. 6, figs. 2, 6, 19) . Dorsal margin short, 

 straight to moderately curved, generally equal to width of attachment 

 scar. On rare specimens, ventroposterior margin flared outward, 

 considerably flattened, forming small, rounded, semicircular, pos- 



