D 



Fig. 10. — Morphology of oysters in the Lopha lugubris group, using specimens 

 o£ L. bellaplicata bellaplicata for illustration (A, C, U.S.N.M. 132222; B, 

 U.S.N.M. 132239; D, U.S.N.M. 8024d). A, External shell morphology of left 

 valve. B, External shell morphology of right valve. C, Spatial divisions of valve 

 referred to in text, D, Interior morphology of right valve. Symbols explained 

 in detail under "Shell Morphology." AA, Anterior auricle. ADM, Anterodorsal 

 margin. AM, Anterior margin. ANS, Anterior slope. AS, Auricular sulcus. 

 ATS, Attachment scar. AVM, Anteroventral margin. AVS, Anteroventral 

 slope. B, Beak. C, Commissure. CR, Crest of valve. D, Denticles. DM, 

 Dorsal margin. DS, Dorsal slope. H, Height of valve. HA, Hinge axis. 

 HP, High point of valve, i. Angle of inclination. ICL, Imbricating concentric 

 lamellae. IPS, Interplical sulcus. L, Length of valve. LCP, Lateral cardinal 

 plate. MCT, Marginal cardinal trough. MF, Midcardinal fold. ML, Micro- 

 lamellae. MP, Median plica. MSD, Maximum diameter of posterior adductor 

 muscle scar. PA, Posterior auricle, paa, Posterior auricular angle. PAS, 

 Posterior adductor muscle scar. PDM, Posterodorsal margin. PLS, Postero- 

 ventral lip of the muscle scar. PM, Posterior margin. PP, Primary plica. 

 PS, Posterior slope. PVM, Posteroventral margin. PVS, Posteroventral slope. 

 R, Resilifer. SC, Subcardinal cavity. SP, Secondary plica. SS, Smooth stage 

 of umbo. U, Umbo. VM, Ventral margin. All figures y^.. 



26 



