PANAMIC-PACIFIC PELECYPODA 437 



JuUacorbuIa biradiata (Sowerby) Plate 75, figures 4-4b 



Corbula biradiata Sowerby, 1833, Proc. Zool. Soc. London, p. 33. "Hab. ad Chiriqui et 



ad sinum caraccensen". — Reeve, 1843, Conch. Icon., vol. 2, Corbula, pi. 1, fig. 



3.— Hanley, 1843, Cat. Rec. Bivalve Shells, p. 47, suppl. pi. 10, fig. 51. 

 Corbula rubra C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, pp. 523, 548. — 



Turner, 1956, Occas. Papers on Mollusks, Mus. Comp. Zool., vol. 2, No. 20, 



pp. 82, 83, pi. 17, figs. 8, 9. 

 Corbula polychroma Carpenter, 1856, Proc. Zool. Soc. London, p. 198 issued Jan. 7th, 



1957. "Hab. in Sinu Californiensi". 

 Aloidis (Caryocorbula) biradiata (Sowerby), Hertlein and Strong, 1950, Zoologica, vol. 



31, pt. 4, pp. 238, 239. 



The shell is small or of medium size, solid, irregularly oblong in shape, 

 somewhat depressed, the wide, flattened umbones and beaks placed a little 

 behind the mid-zone. The anterior side is longer, rounded at the end, the 

 posterior side shorter and subtruncated. The rostrum or posterior-dorsal 

 area is wide, externally limited by a sharp angle. The escutcheon, along the 

 dorsal margin, is narrow and elongated and sculptured only by growth lines; 

 there is no lunule. Surface sculptured with strong, irregular, cordlike con- 

 centrics, continued also on the rostrum. Color white, gray or purple, general- 

 ly with a white ray along each side of the umbone below which the sides 

 of the beak may be purple or red. The interior is often colored with purple 

 on the lateral and ventral margins. Average size about 15 mm., but occa- 

 sional specimens may be larger (length 20.5 mm.). 



Length 15 mm., height 10.6 mm., diameter of a right valve 3.7 mm. 

 Bucaro, Panama. 



Easily recognized by its flattened, subrectangular shape, and by its 

 colored umbones and beaks. 



Range — Gulf of California to northern Peru. Panama: Pearl Islands; 

 Bucaro; San Carlos; Panama City. Colombia: Isla del Gallo. Ecuador: 

 Manta; Santa Elena. Peru: Tumbez; Mancora; Paita. 



Jnllacorbnia ecuabula (Pilsbry and Olsson) 



Corbula ecuabula Pilsbry and Olsson, 1941, Proc. Acad. Nat. Sci. Philadelphia, vol. 93, 

 p. 75, pi. 12, figs. 3, 4, 5. 



Shell of medium size, moderately thin, strongly inequilateral, and 

 subequivalve. The umbones and beaks are placed at the posterior third, the 

 anterior side, therefore, much longer, its dorsal margin descending slightly 

 so that the outline of the valve is oblique. The margin of the short pos- 

 terior side slopes down sharply, its rostrum narrow, bounded outwardly by 

 a weak keel or angle only. The left valve is a little smaller than the right 

 with a depressed ray in the ventral region. Surface smooth or marked with 

 coarse concentrics, stronger on the anterior side and over the rostrum. 



Length 16.25 mm., height 12 mm., diameter of a right valve 3.7 mm. 

 Fossil, Punta Blanca, Ecuador. 



Length 18.1 mm., height 11.3 mm., diameter of a left valve 3.6 mm. 

 Zorritos, Peru. 



This species was first described as fossil from the Pliocene of Ecuador 

 but a few Recent specimens have also been collected. It is distinguished from 

 its allies by its oblique shape and extreme posterior position of its beaks. 



Range— Cozst of Peru and Ecuador. Ecuador: Punta Blanca, Peru: 

 Zorritos. 



