436 AXEL A. OLSSON 



Key to Panamic-Pacific species 



I. Shell of square-ovate or rectangular form, subequilateral, the beaks 



placed near the middle. 

 A. The rostral angle is high and sharp, the rostrum itself wide. 



1. Shell small, solid, convex, with a squarish ovate form. Surface strongly- 

 sculptured. 



/. bicarinata 



2. Shell larger, longer, and thinner. Sculpture finer. 



/. elenensis 

 B'. Rostral angle lower, the rostrum narrower. 



3. Shell elongated ovate, solid, white with colored rays along the umbones 

 and in the interior. 



/. biradiata 

 II. Shell obliquely oblong in shape, strongly inequilateral, the beaks placed 

 nearer the posterior end. 



4. Shell of moderate weight, the rostral area low. 



/. ecuabula 



JaKacorbnla bicarinata (Sowerby) Plate 75, figures 6-6b 



Corbula bicarinata Sowerby, 1833, Proc. Zool. Soc. London, p. 35. "Hab. ad littora 

 Columbiae Occidentalis." "Found in sandy mud at from seven to seventeen 

 fathoms at Panama, Real Llejos, Caraccas and St. Elena." Panama was desig- 

 nated as type locality by Hertlein and Strong. — Hanley, 1843, Cat. Rec. Bivalve 

 Shells, p. 46, appendix pi. 12, fig. 31. West Colombia. — Reeve, 1844, Conch. 

 Icon., vol. 2, Corbula, pi. 3, fig. 23. 



Aloidis (Caryocorbula) bicarinata (Sowerby), Hertlein and Strong, 1950, Zoologica, 

 vol. 35, pt. 4, p. 238. 



Shell small, solid, squarely ovate, nearly equilateral, the anterior side 

 somewhat longer, rounded at the end, the posterior side shorter, abruptly 

 truncated, and flattened. The posterior-dorsal area or rostrum is wide, 

 depressed and outwardly set apart by a sharp angle or keel, and usually 

 carrying a radial mid-rib enclosing a deep, smooth, escutcheon-like depres- 

 sion. There is also a sunken, plain area on the anterior side of the beak 

 suggestive of a lunule. The valves are of nearly equal size and sculptured 

 with coarse, concentric cords; on the rostrum the cords are finer and more 

 close-set. Color white, the growing edge of the valves generally brown. 



Length 11.2 mm., height 8 mm., diameter 2.7 mm. (left valve). 

 Venado Beach, Panama Canal Zone. 



This is a characteristic species, easily recognized by its rectangular 

 form, sharply truncated posterior margin and neat sculpture. It is similar 

 to J. scutata Gardner^^ from the Pliocene of Florida and North Carolina, 

 but is generally somewhat larger. Corbula {Cuneocorbula) ira Dall, 1908, 

 "Albatross Report" (Bull. Mus. Comp. Zool., vol. 43, No. 6, p. 423), 

 hitherto unfigured (see Plate 76, figure 5), was described from specimens 

 dredged in the Gulf of Panama from a depth of 182 fathoms. This shell 

 resembles /. bicarinata and perhaps should be united with it. 



Range — Gulf of California to nurrnern Peru. Panama: Panama City; 

 Bucaro. Panama Canal Zone: Venado ueacn. Colombia: Isla del Gallo, 

 Ecuador: Isla la Plata. Peru: Zorritos. 



iSGardner, 1943, Prof. Paper 199-A, U.S. Geol. Survey, pp. 140, 141, pi. 23. figs. 26, 

 30 - 32.— Olsson and Harbison, 1953, Mon. Acad. Nat, Sci. Philadelphia, No. 8, p. 149, 

 pi. 7, fig. 6. 



