252 AXEL A. OLSSON 



1834, Conch. Illust., Cardium, p. 3, No. 38, fig. 17.— Reeve, 1844, Conch. Icon., 

 vol. 2, Cardium, pi. 8, fig. 43. 

 Cardium {Trigoniocardia) grmiiferum Broderip and Sowerby, Hertlein and Strong, 

 1947, Zoologica, vol. 31, pt 4, p. 143. — Hertlein and Strong, 1955, Bull. Amer. 

 Mus. Nat. Hist., New York, vol. 107, art. 2, p. 186. 



Shell relatively small, 15 mm. or less high. Ribs number about 20 of 

 which those on the middle are high, narrow, triangular in section and separ- 

 ated by wide, deep, strongly cross-threaded intervals; the ribs on the pos- 

 terior slope usually number about 11, are smaller and close-set. Summit of 

 the ribs smooth or with scattered nodes. 



Length 14.6 mm., height 15 mm., diameter 12 mm. Esmeraldas, Ecuador. 



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

 San Carlos. Ecuador: Manta; Esmeraldas; Santa Elena. Peru: Zorritos. 



Subgenus A^fERICARDIA Stewart, 1930 



Type species by original designation, Cardium medium Linne, Recent, 

 West Atlantic. 



Shell solid, quadrate in shape, with high, wide umbones, the posterior 

 side flattened, the umbonal angle high and sharp, the posterior margin 

 truncated. Ribs are flat-topped, rectangular in section, the interspaces be- 

 tween them narrow and deep. Ribs covered by a periostracal layer of coarse, 

 imbricated scales, easily worn off. Interspaces are finely cross-threaded. 



Trigoniocardia (Americardia) gnanacastense (Hertlein and Strong) 



Plate 37, figures 9, 9a 



Cardium planicostatum Sowerby, 1833, Proc. Zool. Soc. London, p. 83. (Not Cardium 



planicostatum Sedgwick and Murchison, 1829). — Sowerby, 1840, Conch. Illust. 



Cardium, p. 7, No. 83, fig. 25. — Reeve, 1844, Conch. Icon., vol. 2, Cardium, pi. 



6, fig. 31. 

 Cardium {Americardia) gunacastense Hertlein and Strong, 1947, Zoologica, vol. 31, Pt. 



4, pp. 140, 141. 



The reason for the renaming of this species is discussed by Hertlein and 

 Strong. Sowerby's type of C. planicostatum must remain the type of T. 

 guanacastense. 



The shell is often large (to about 50 mm.), solid. Ribs generally about 

 30 and when fresh, the surface is covered with close-set, concentric imbri- 

 cation which scale off easily after a slight amount of beach wear. The in- 

 terior of the shell is white. 



Length 34.7 mm., height 43.2 mm., diameter 34.6 mm. San Pedro near 

 Manglaralto, Ecuador. 



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

 Ecuador: Sua; Charapota; Manta; Isla la Plata; Manglaralto; Santa Elena; 

 Punta Mambri. Peru: Mancora. 



Subgenus APIOCARDIA, new subgenus 



Type species Cardium ob ovale Sowerby. 



Shell elongately subovate, the umbonal axis strongly inclined so that 

 the umbones and beaks are distinctly anterior in position. Posterior side 



