PANAMIC-PACIFIC PELECYPODA 245 



7. Shell rounded, the length and height nearly the same, the posterior 

 side not contracted. Hinge provided with lateral teeth. 



Genus Microcardium 



Subfamily TRACHYCARDIENAE 

 Genus TJRACHYCARDIUM Morch, 1853 

 Type species by subsequent designation, von Martens, 1870 Cardiit/m 

 isocardia Linne. West Atlantic. 



Shell subovate, usually higher than long, convex, with large, full um- 

 bones (submedian) ending in small, adjacent, orthogyrate beaks. The sculp- 

 ture is produced by large, elevated, radial ribs, covered in whole or in part, 

 with imbricated scales, spines or noded, ribbon-like cords, usually best 

 developed on the flanks. Hinge stout, usually with two cardinal teeth, of 

 which one is large and prong-shaped, the other above it small, the socket 

 between them large. The lateral teeth are large and spaced equidistant from 

 the middle of the hinge. Margins deeply grooved by the ends of the ribs. 



The genus Trachycardium is divisible into three subgenera on basis of 

 the ornamentation of the ribs. 



I. Ribs covered completely with coarse, vaulted, imbricated scales pro- 

 ducing a harsh, rasplike surface. 



Subgenus Trachycardiv/m, s.s. 



II. Posterior edge of each rib enlarged and elevated into a high, tuberculate 

 cord or ribbon. 



Subgenus Phlogocardia 

 HI. Ornamentation of the ribs weaker, reduced largely to small scales or 

 nodes, strongest on the side ribs, the ribs in the mid-zone and on the 

 umbones largely smooth. 



Subgenus Dallocardia 



Trachycardium (Trachycardium) consors (Sowerby) Plate 37, figure 1 



Cardium consors Sowerby, 1833, Proc. Zool. Soc. London, p. 85. — Sowerby, 1840, Conch. 



Illust. Cardium, p. 3, No. 40, fig. 8.— Reeve, 1845, Conch. Icon., vol. 2, Cardium, 



pi. 17, fig. 86. 

 Cardium {Trachycardium) consors Sowerby, Maxwell Smith, 1944, Panamic Marin* 



Shells, p. 58, figs. 735, 745, 746.— Hertlein and Strong, 1947, Zoologica, vol. 31, 



pt. 4, p. 147. 



Shell ovate, generally higher than long, with solid, highly convex valves 

 and wide, full umbones, nearly median in position, the small beaks touching 

 over the dorsal margin. Ribs high and strong, usually about 31 in number, 

 rectangular in section and separated by deep, narrow interspaces, orna- 

 mented with elevated, inverted, U-shaped scales, coarsely imbricated on 

 the anterior set of ribs, thinner and higher on the middle posterior set; on 

 the latter, the posterior arm of each scale unites and joins the scale in 

 front so as to form a high, curiously flattened, straight wall. Color a creamy 

 white mottled with yellow and purple. 



Length S6 mm., height 66.6 mm., diameter 57.5 mm. Pearl Islands, 

 Panama. 



This fine cockle is distinguished from all others of the region by the 

 coarse, rasplike surface of its ribs. The species is related to T. emmonsi 

 (Conrad), a fossil from the Pliocene of the Carolinas and Florida. T. 

 isocardia (Linne), a Recent species from the West Indies, has weaker 

 sculpture. 



