PANAMIC-PACIFIC PELECYPODA 179 



Flacnanomia panamensls Olsson 



Placuanomia panamensis Olsson, 1942, Bull. Amer. Paleont., vol. 27, No. 106, pp. 183, 

 184, pi. 1, figs. 1, 4, 5. 



Shell of moderate or large size, rounded or subovate, with the white, 

 silvery, micaceous texture of Anomia. The lower valve is attached directly 

 by a broad area of the umbone, its counterpart indicated on the upper valve 

 as a flattened area without sculpture. Sculpture of the free surface is formed 

 by small, radial threadlets which may become partly obscured or obsolete 

 along the margins by irregular concentrics. In general, the surface is flat 

 with low, irregular undulations around the margins only. 



Range — Panama. Canal Zone: Balboa; Amador Beach. 



Order HETEREDONTIDA 

 Superfamily ASTARTACEA 

 Family CRASSATELLIDAE 



Shell porcellaneous, solid, subtriangular to oblong, with convex or 

 compressed umbones, the anterior side shorter, higher and rounded, the 

 posterior contracted, flattened, pointed, or subtruncate. Hinge strong with 

 large cardinal teeth and laterals. Ligament internal, attached to a resilifer 

 groove between the cardinal teeth. Surface smooth or with growth line 

 sculpture, sometimes concentrically undulate especially over the umbones. 

 Pallial line simple, the adductor scars usually impressed. Ventral margin 

 smooth or crenate. 



Two genera. 



I. Shell large, elongate, the posterior end recurved, pointed. 



Genus Eucrassatella 



II, Shell small to minute, subtrigonal. 



Genus Crassinella 

 Genus EUCRASSATELLA Iredale, 1924 



Type species by original designation, E. kingicola Lamarck. Recent. 



Australia. 



Shell solid, elongate-subtrigonal, the posterior side contracted and 

 pointed, the anterior end more rounded. Lunule and escutcheon distinct, 

 deeply impressed. Hinge margins heavy, the ligament internal, lodged in a 

 deep resilifer. Left valve with two, the right with three cardinal teeth, the 

 marginal ones becoming effaced by the resilium or merging with the dorsal 

 edge. Lateral margins above the muscle scars thickened or grooved to serve 

 as pseudolaterals. Muscle scars deep, connected by a simple pallial line. 

 Ventral margins smooth. Beaks more or less distinctly opisthogyrate. Um- 

 bones flattened or rounded, the external sculpture principally concentric, 

 strongest near the beaks. — [Olsson and Harbison, 1953.] 



Subgenus HYBOLOPHUS Stewart, 1930 

 Type species by original designation, Crassatella gibbosa Sowerby. 

 Two cardinal teeth in each valve. Umbones and beaks tilted or pointed 

 backwards (opisthogyrate), the surface near the tip of the umbones strongly 

 flattened and sculptured with wavelike, concentric undulations. 



Eucrassatella (Hybolophus) gibbosa (Sowerby) Plate 25. figures 1-lb 



Crassatella gibbosa Sowerby, 1832, Proc Zool. Soc. London, p. 56 (St. Elena and 

 Xipixapi). — Reeve, 1843, Conch. Icon., vol. 1, Crassatella, pi. 1, figs, la, lb. 



