PANAMIC-PACIFIC PELECYPODA 95 



The shell is generally large (up to 55 mm.), convex, subquadrate, in- 

 equivalve, with full, nearly medial umbones and usually quite thin. The 

 posterior submargin is strongly flattened as if truncated almost at right 

 angles. The left valve has 28 to 30, large ribs, flat, smooth and separated 

 only by lined interspaces on the middle and posterior surfaces, strongly 

 noded and with wider interspaces on the anterior portion; the ribs on the 

 umbone are finely beaded throughout. Right valve is similar but the ribbed 

 interspaces are wider. Cardinal area is longer than high, smooth. 



Carpenter's type of A. bifrons in the British Museum (Nat. Hist.) is 

 herein figured; its dimensions are as follows: length 37.9 mm., height 30.8 

 mm. diameter of the closed valves 27.5 mm. A. bifrons is a larger species 

 than A. aequatorialis, and of a more rhombic form, the posterior side so 

 strongly impressed or flattened so as to appear as if cutoff sharply, the ven- 

 tral and anterior margins meeting to form a right angle. Allied closely to A. 

 brasiliana Lamarck (incongrua Say) of the western Atlantic, the Pacific 

 shell is generally smaller, more rhombic in shape, and the sculpture is 

 smoother. 



Range — ^Gulf of California to northern Peru. Panama: Guanico; Bucaro. 

 Colombia: Isla del Gallo. Ecuador: Galeras; Mompiche. Peru: Tumbez; 

 Zorritos; Paita (D'Orbigny). 



Anadara (Cunearca) aequatorialis (d'Orbigny) Plate 9, figures 4, 4a, 5, 5a 



Area ovata Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 8, fig. 49. Santa Elena, Ecuador. 

 Not A. ovata Gmelin, 1791. 



Area aequatorialis d'Orbigny, 1846, Vol. Amer. Merid., vol. 5, p. 636. New name for 

 A. ovata Reeve, not of Gmelin, 1791. 



Seapharca (Cunearea) aequatorialis d'Orbigny, Maury, 1922, Paleont. Amer., vol. 1, 

 No. 4, p. 34, pi. 3, figs. 2, 9. — Hertlein and Strong, 1943, Zoologica, vol. 28, 

 pt. 3, p. 160. 



Anadara (Cunearea) aequatorialis (d'Orbigny), Reinhart, 1943, Special Paper, Geol. 

 Soc. America, No. 47, pp. 69, 70. — Rost, 1955, Allan Hancock Pacific Expedi- 

 tions, vol. 20, No. 2, pp. 206, 207, pi. 15, figs, a-c; text-figs. 92 a-c. 



Area subelongata Nyst, 1848, Mem. Acad. Royale Sci., Lettres, Beaux-Arts Belgique, t. 

 221, p. 70. 



The shell is of medium size, relatively thin to slightly thickened, sub- 

 ovate and slightly inequivalve, the anterior side rounded and somewhat 

 produced, the posterior side flattened, its margin appearing obliquely 

 truncated, its end somewhat pointed. Umbones wide and prominent with 

 a slight depression extending along the front of the umbonal angle towards 

 the ventral margin. Ribs on the left valve number 30, the anterior set of 

 10 are rather coarsely noded throughout, the rest finely noded or smooth. 

 The ribs on the right valve are narrower and separated by wider inter- 

 spaces, the anterior ones noded, the rest plain. 



The shell is relatively thin at first becoming heavier with age. Our 

 largest specimen, a shell from Sua, Ecuador, has a length of nearly 44 mm. 

 and is heavy. This species with bifrons seem to form an intergradational 

 series and at times specimens are difficult to separate. A. aequatorialis 

 seems to be more common south of Panama. 



Range — Panama southward to Peru, perhaps northward to the Gulf 

 of CaHfornia. Panama: Bucaro. Ecuador: Sua; Mompiche; Limones; Manta; 

 Santa Elena. Peru: Tumbez; Zorritos; Boca Pan. 



