PANAMIC-PACIFIC PELECYPODA 251 



A. Shells small or of medium size. Without a deciduous outer layer cov- 

 ering the summit of the ribs which are, therefore, smooth, beaded or 

 with scattered nodes. Intervals between the ribs coarsely pitted or 

 cross-threaded. Contour of shell generally rounded. 



Trigoniocardia, s.s. 



R Shells of medium-size, high, quadrate in form. Ribs strong, rectangular 

 in section, their interspaces narrow. Summit of ribs covered by a 

 deciduous layer of closely imbricated scales, easily destroyed by wear. 

 Intervals between the ribs with fine cross threads. 



Subgenus Americardia 



II. Shells obliquely ovate, the umbones and beaks inclined towards the 

 anterior side. Posterior side truncate, its surface flat or slightly con- 

 vex, no medial sulcation. Anterior lateral teeth crowded against the 

 cardinals. 



Subgenus Afiocardia 



Subgenus TRIGONIOCARDIA s.s. 

 Shell rounded or subovate in shape, the posterior side short and narrow, 

 flat or deeply impressed, its margin as if sharply truncated. The ribs are 

 low, round-topped or high and narrow, their intervals marked with coarse 

 cross threads or deeply pitted. Surface of ribs may be smooth, beaded 

 or noded. Periostracum lacking. 



Two species are regional, T. biangtdata has generally been referred to 

 Americardia but its shape is like that of T. granijera and the ribs are not 

 covered by a layer of imbricated scales. 



A. Shell of medium size, height 30 mm. Ribs low, rounded, close-set, smooth 

 or somewhat granose on the anterior side. Interior of shell generally 

 colored a purple-red. 



T. biangulata 



B. Shell small, height about 15 mm. Ribs high, narrow, between widely 

 grooved interspaces, smooth or finely beaded. Interior of shell white. 



T. granijera 



Trigronioeardia (Trigoniocardia) biangulata (Broderip and Sowerby) 



Plate 37, figures 6, 6a 



Cardium biangulatum Broderip and Sowerby, 1829, Zool. Jour., vol. 4, p. 367. — Sowerby, 



1840, Conch. Illust. Cardium, p. 7, No. 82, fig. 2.— Reeve, 1844, Conch. Icon., 



vol. 2, Cardium, pi. 6, fig. 29. 

 Cardium (Fraffum) biangulatum Broderip and Sowerby, Maxwell Smith, Panamic 



Marine Shells, p. 58, fig. 747. 

 Cardium {Americardia) biangulatum Broderip and Sowerby, Hertlein and Strong, 1947, 



Zoologica, vol. 31, pt. 4, p. 140. 



Shell of medium size, with prominent, convex umbones and well rounded 

 anterior side. Ribs low, rounded, close-set, the narrow interspaces closely 

 and regularly cross-threaded. Interior colored with pink or mahogany red. 



Length 31.6 mm., height 29.3 mm., diameter 23 mm. Pearl Islands, 

 Panama. 



Range — Gulf of Califonia to Ecuador. Panama: Pearl Islands. Ecuador: 

 Manta; Santa Elena. 



Trigoniocardia (Trigoniocardia) granlfera (Broderip and Sowerby) 



Plate 38, figure 3 



Cardium graniferum Broderip and Sowerby, 1829, Zool. Jour., vol. 4, p. 367.— Sowerby, 



