44 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



variation and ontogenetic series, fossil "populations," and most North 

 American types of the species. Numerous additional fragments. 



General form. — Summary of measurements presented in table 2. 

 Shell attaining moderate size, average size decreasing from south 

 (Texas) to north (Colorado) (fig. 14a, c) ; inequivalve, left valve 

 slightly larger, much more convex than right ; slightly to moderately 

 inequilateral, prosocline to acline. Outline commonly round to ovate, 

 subquadrate, rarely triangular (pis. 3-6; pi. 3, figs. 1, 3, 5, 9-15 

 typical) ; height slightly greater than length on majority of specimens. 

 Anterior, ventral margins straight to slightly curved; ventrolateral 

 margins moderately curved ; posterior margin with moderately convex 

 curvature in absence of auricle, moderately concave beneath auricle 

 when developed. Dorsolateral margins normally straight to slightly 

 curved, gently inclined (pi. 3, fig. 3), posterodorsal margin longest, 

 equaling two-thirds to slightly over one-half total length of shell. 



Table 2. — Summary of measurements for Lopha bellapHcata bellaplicata (Shumard) 



Character Valve 

 Height (H) J^ 



Length (L) \^ 



Width (W) 1^ 



Percent valves with H > L LR 



Percent valves with H=:L LR 



Percent valves with H < L LR 



Area, inscribing rectangle of valve...) 



Length, beak to posterior margin 

 (LBP) ^ 



Ratio, LBP : L L 



Angle between dorsal and dorso- 



posterior margins L 



Angle of inclination (i) LR 



Percent of specimens with observable 



attachment scar L 



Height of attachment scar (HATS) . . L 

 Length of attachment scar (LATS) . . L 

 Area, inscribing rectangle of attach- 

 ment scar (HATS X LATS) L 



Height of smooth portion of shell 

 dorsad to plicate ornamentation. . . . ) 



