PANAMIC-PACIFIC PELECYPODA 253 



truncate, flattened or slightly convex but the posterior margin is straight, 

 nonemarginate. Ribs strong, usually smooth, flattened on top, sometimes 

 with scattered nodes, the interspaces coarsely cross-threaded. Hinge with 

 the anterior lateral teeth crowded against the cardinals. 



Trj^oniocardia (Apiocardia) obovale (Sowerby) Plate 38, figure 4 



Cardium obovale Sowerby, 1833, Proc. Zool. Soc. London, p. 84. — Sowerby, (1840?) 



Conch. Illust. Cardium, p. 7, No. 90, fig. 4. — Reeve, 1845, Conch. Icon., vol. 2, 



Cardium, pi. 21, fig. 117. 

 Cardium ovuloides Reeve, 1845, Conch. Icon., vol. 2, Cardium, pi. 22, fig. 126. 

 Trigoniocardia obovale (Sowerby), Maxwell Smith, 1944, Panamic Marine Shells, p. 



59, fig. 736. 

 Cardium (Trigoniocardia) obovale Sowerby, Hertlein and Strong, 1947, Zoologica, vol. 



31, pt. 4, p. 144. — Hertlein and Strong, 1955, Bull. Araer. Mus. Nat. Hist., New 



York, vol. 107, art. 2, p. 187. 



The shell is usually small, less than 23 mm. in height. Ribs number 

 between 20 or 21, largest along the umbonal slope and just in front of it. 

 The ribs are obliquely flattened, their detailed sculpture varying considerably. 

 In beach specimens, the ribs are smooth because of wear, but in well-pre- 

 served shells, the surface is strongly sculptured, the corners of the ribs and 

 the interspaces being etched with deep, incised lines and cross threads. 

 To such a strongly sculptured specimen. Reeve gave the name ovuloides. 



Length 15 mm., height 16 mm., diameter 15.6 mm. Zorritos, Peru. 



This is a common and widely distributed species. Several related forms 

 occur as fossil, the largest and finest being the T. cabofasada (Pilsbry and 

 Olsson) from the Pliocene of Ecuador which attained a height of 38 mm., 

 the summit of the ribs of which are coarsely noded. 



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

 San Carlos; Biicaro; Guanico. Ecuador: Esmeraldas; Galeras; Manta; Puerto 

 Gallo; Santa Elena. Peru: Tumbez; Zorritos; Mancora. 



Subfamily PROTOCARDIDfAE 



Genus MICKOCARDIUM Thiele, 1934 



Type species by subsequent designation, Keen, 1937, Cardium (Fulvia) 

 peramabile Dall. Recent, Florida and the Caribbean. 



Shell generally small, thin and delicate, subcircular to subovate, with 

 large, convex, subcentral umbones. Sculpture is formed by numerous, small 

 riblets, their interspaces cross-threaded, enclosing deep pits between them, 

 the posterior set of riblets set apart from the others by their smaller size 

 and by their more finely cross-threaded intervals, some of which carry small 

 granules or spinules, easily broken off. The hinge is normal to the family. 

 Most plentiful in moderately deep waters. 



There are two species regional. 



I. Shell rounded to subovate, the posterior side narrow and sharply 

 truncated at the margin. Posterior set of granules are small. 



M. panamemis 



II. Shell subelongate, the posterior side longer and narrower. Riblets num- 

 erous, the posterior set of granules fairly coarse. 



M. -pazianum 



