PANAMIC-PACIFIC PELECYPODA 435 



I. Shell large, (length 27 mm.), moderately heavy. Beaks submedian, 

 the anterior side somewhat longer. 



P. inflata 



II, Shell generally smaller (length 22 mm. or less), roundly convex, sub- 

 cylindrical, thinner, the beaks a trifle more anterior in position, the 

 posterior end hence longer. 



P. cylindrica 



Panamicorbnla inflata (C. B. Adams) Plate 76, figures 1-lc 



Potamomya inflata C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New Yoric, pp. 520, 



No. 500, p. 548. 

 Potamomya aequalis C. B. Adams, 1852, idem., pp. 519, 520, No. 499; pp. 547, 548. 

 Potamomya trigonalis C. B. Adams, 1852, idem., p. 520, No. 501; p. 548. 

 Corbula macdonaldi Dall, 1912, Smith. Misc. Coll., vol. 59, No. 2, p. 3.— Dall, 1925, 



Proc. U. S. Nat. Museum, vol. 66, art. 17, No. 2554, p. 15, pi. 17, fig. 1, 3. 



Shell large, moderately heavy, with subequal ovate valves and high 

 prominent umbones. The anterior side is a little longer than the posterior. 

 An adult right valve measures: length 26.9 mm., height 21.7 mm., diameter 

 9.6 mm. Dall's Corbula macdonaldi said to have been collected frcm the 

 Pleistocene muck beds at Colon (loc. 5848), probably came from the Pacific 

 side of the isthmus. 



Range — Mazatlan to northern Peru. Panama Canal Zone: Farfan 

 Beach; Palo Seco. Colombia: Isla del Gallo. Ecuador: Limones; Puerto Pal- 

 mar (Colonche). Peru: Tumbez. 



Fanamicorbula cylindrica Morrison Plate 76, figures 2, 2a 



Panamicorbnla cylindrica Morrison, 1946, Smith. Misc. Coll., vol. 106, No. 6, pp. 47, 48, 



pi. 1, figs. 15, 17. 

 Panamicorbnla inflata (C. B. Adams), Voices, 1945, Bull. Amer. Museum Nat. Hist, 



vol. 86, No. 1, pp. 11, 12, pi. 2, figs. 1-4. (Not inflata C. B. Adams.) 



This is a smaller and thinner species than P. inflata, with more anterior 

 beaks, the posterior side hence longer. Although the valves are strongly 

 convex, the umbones seem relatively low, the shell, therefore, assuming an 

 apparent ovate-cylindrical form. The species is generally found associated 

 with C. inflata and in the same environment. 



Length 22 mm., height 16.3 mm., diameter 16 mm. Rio Marina man- 

 grove swamp, San Jose Island, Pearl Islands (Morrison, USNM). 



Range — Panama to northern Peru. Panama: San Jose Island, Pearl 

 Islands; Bucaro. Panama Canal Zone: Palo Seco. Ecuador: Limones. Peru: 

 Tumbez. 



Genus JTJLIACOKBULA Olsson and Harbison, 1953 



Type species by original designation: CorbtUa cubaniana d'Orbigny 

 (==C, knoxiana C. B. Adams). Recent, Florida southward through the 

 West Indies and the Caribbean to Panama, 



Shell small or medium-sized, thin or heavy, rhombic to subrectangular, 

 the anterior side rounded, the posterior side sharply truncate. Posterior- 

 dorsal area is well defined, generally wide and strongly sculptured, en- 

 closing a small, lanceolate escutcheon along the dorsal margin, externally 

 limited by a sharp angle, ridge or keel. No lunule, but the area below the 

 beaks is often deeply impressed. Hinge as in Caryocorbula, Surface sculp- 

 tured with medium or coarse, regular concentrics, similar in each valve. 



