6o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



terior auricle separated from main body of shell by a broad, shallow, 

 indistinct auricular sulcus, generally a broadened interplical sulcus or 

 2 sulci with the intermediate plication greatly reduced. 



Right valve flat to slightly arched ; convexity greatest in umbonal 

 region; flanks flat, rarely concave near margin when ventral edge 

 upturned. Left valve moderately to highly convex, convexity greatest 

 at upper edge of attachment scar where prominent ; otherwise crest 

 and high point situated medially on lower third of valves. Anterior 

 slope typically steep, ventral slope shallow, posterior slope steep 

 dorsally, moderate to gentle or irregular ventrally, depending on devel- 

 opment of posterior auricle. 



Table 4. — Representative measurements of right valves associated with Lopha 

 bellaplicata bellaplicata var. A and possibly belonging to this form. 



U.M.M.P. U.M.M.P. 



Character 43406 43413 



Height (H) 19.1 mm. 16.7 mm. 



Length (L) 9.6 mm. 15.8 mm. 



Width (W) 3.5 mm. 4.8 mm. 



Height, cardinal area 2.2 mm. 



Length, hinge line 3.9 mm. 



Width, midcardinal fold 1.9 mm. 



Height, denticulate margin 7.1 mm. 



Number of denticles in 5 mm. distance 11 



Maximum diameter of muscle scar 6.9 mm. 



Minimum diameter of muscle scar 3.6 mm. 



Distance (height), dorsal edge of muscle scar 



to beak 8.1 mm. 



Angle of inclination (i) 82° 61° 



Number of major lamellae in 5 mm. height 



(midvalve) 3 



Beaks and umbos. — Beak, umbo unknown on left valve, obscured 

 by attachment scar, apparently slightly recurved, orthogyre to slightly 

 opisthogyre. Beak of right valve known from numerous, nearly smooth, 

 associated upper valves; pointed to narrowly rounded, smooth, nor- 

 mally opisthogyre, moderately recurved. Umbone gently arched, in 

 some valves separated from main body of shell by a constriction or 

 large lamella. 



Attachment scar. — Area of attachment terminal, small to medium 

 size, round to subovate, flat to slightly concave, steeply inclined or 

 vertical relative to plane of commissure, rarely moderately inclined. 

 Scar surface smooth or with faint concentric markings of shell to 



