PANAMIC-PACIFIC PELECYPODA 247 



Shell subcircular to subovate, with moderately convex valves. The ribs 

 are small and usually number about 35. Imbrication of the ribs is formed 

 by relatively small scales, sometimes partly spinous on the posterior slope 

 and confined mostly to the marginal areas, the middle ribs smooth. Color 

 creamy white, mottled with purple and yellow. 



Length 48.2 mm., height 49.6 mm., diameter 36.8 mm. Manta, Ecuador. 



A common and widely distributed species differing from T. consors by 

 its more rounded, less convex valves, and weaker ribs; the umbonal ribs 

 are usually smooth. 



Range — Lower California to northern Peru. Panama: Panama City; 

 Burica Peninsula; Pearl Islands. Colombia: Isla del Gallo. Ecuador: Manta; 

 Santa Elena. Peru: Zorritos; Mancora; Lobitos; Negritos; Paita; Bay of 

 Sechura. 



Genus MEXICARDIA Stewart, 1930 



Type species by original designation, Cardium procerum Sowerby. 



Shell high or broadly ovate, convex, the dorsal slopes rounded, with 

 high, prominent umbones and nearly central, orthogyrate beaks. Adult 

 sculpture is formed by large, flattened, smooth ribs separated by grooved 

 interspaces; young specimens have sharply triangular ribs bearing small 

 scales. Hinge heavy, with two cardinal teeth in each valve of which the 

 right posterior and the left anterior teeth are large and pointed, the other 

 cardinal teeth small; the lateral teeth are strong and placed equally distant 

 from the middle of the hinge. Posterior margins of the shell deeply serrated 

 by the ends of the ribs. Color of shell beneath the brown periostracum is a 

 dingy white variegated by brown. 



>Iexicardia procera (Sowerby) Plate 37, figure 4 



Cardium procerum Sowerby, 1833, Proc. Zool. Soc. London, p. 83. Real Llejos. — Sowerby, 



1840, Conch. Illust, Cardium, p. 5, No. 61, fig. 23.— Reeve, 1844, Conch. Icon., 



vol. 2, Cardium, pi, 10, fig. 51. 

 Cardium laticostatum Sowerby, 1833, Proc. Zool. Soc, London, p. 85. Xipixapi, Ecuador. 



— Sowerby, 1840, op. cit., p. 1, fig. 30. 

 Cardium panamense Sowerby, 1833, Proc. Zool, Soc. London, p. 85. Panama, — Sowerby, 



1840, op. cit., p, 5, sp, 62, fig, 21.— Reeve, 1844, op. cit., pi. 11, fig. 56. 

 Cardium rotundatum Carpenter, 1857, Cat Mazatlan Shells, Brit Mus., p. 531, No. 687 



(young shell). 

 Cardium dulcinea Dall, 1916, Proc. U. S. Nat. Mus., vol. 52, No. 2182, pp. 412, 413. 

 Trigoniocardia eudoxia Dall, 1916, op. cit., p. 412 (young shell). 

 Cardium (Mexicardia) procerum Sowerby, Hertlein and Strong, 1947, Zoologica, vol. 



31, pt. 4, pp. 142, 143. 



Shell often large (height 100 mm. or more), solid, with coarse, convex, 

 ovate valves. Umbones full and prominent, the beaks located nearly midway. 

 Ribs large, numbering from 22 to 25, low, rounded, or flattened between 

 deeply grooved interspaces; ribs in the young shell have a triangular section 

 and bear small scalelike spines. Periostracum coarse, brownish, the color 

 of the shell underneath white mottled or variegated with brown. Posterior 

 margins of the valves deeply serrated by the ends of the ribs. 



Length 89 mm., height 99 mm., diameter 82 mm. Bayovar, Peru. 



This is a common and widely distributed species ranging from the Gulf 

 of California to northern Chile; the most southerly record is at Bahia de La 

 Independencia (lat. 14° IS' S) in middle Peru, Peruvian specimens are as 



