PANAMIC-PACIFIC PELECYPODA 415 



diameter 17.6 mm. (a left valve). The species occurs as fossil in the 

 Pliocene of Ecuador. 



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

 Carlos; Panama City. Colombia: Isla del Gallo. Ecuador: Punta Ostiones 

 (Esmeraldas); Mompiche; Puerto Callo. Peru: Mancora; Boca Pan; 

 Tumbez. 



Psammacoma elytmm (Keen) Plate 74, figure 7 



Tellina elongata Hanley, 1844, Proc. Zool. Soc. London, p. 144. — Not T. clongata Dillwyn, 



1823.— Hanley, 1846, Thes. Conch., vol. 1, p. 302, No. 156, pi. 62, fig. 199 



Chiriqui, West Columbia. — Sowerby, 1867, Conch. Icon., vol. 17, Tellina, pi. 25, 



fig. 137. 

 Macoma [Psammacoma) elongata (Hanley), Hertlein and Strong, 1949, Zoologica, vol. 



34, pt. 2, pp. 89, 90. — Hertlein and Strong, vol. 1955, Bull. Amer. Mus. Nat. 



Hist., vol. 107, art. 2, p. 200. 

 Macoma (Psammacoma) elytrum Keen, 1958, Bull. Amer. Paleont., vol. 38, No. 172, 



p. 244, pi. 30, fig. 14. New name to replace T. elongata Hanley, preoccupied by 



T. elongata Dillwyn, 1823. 



Shell elongate-quadrate, the anterior side about a third longer than 

 the posterior, somewhat expanded, highest and most inflated along the 

 umbonal slope, slightly impressed across the anterior-ventral side; the 

 shorter posterior side is narrowed, slightly flexed, rounded, or weakly 

 pointed at the end and slightly gaping. The valves are thin, white, sub- 

 translucent, smooth and often polished, covered with minute lines of 

 growth which sometimes may show a play of weak, iridescent colors; the 

 covering periostracum is thin and of an ashy gray or dirty straw color. 

 The pallial sinus is of moderate size, extends well beyond the middle of 

 the valves, highest under the beak, and partly confluent with the pallial 

 line below. The hinge is weak, the scar of the ligament long. 



Length 46.4 mm., height 2.'?.9 mm., diameter of a right valve 6.6 mm. 



Length 5L8 mm., height 28.7 mm., diameter 15.1 mm, Panama Bay 



Distinguished by its elongated thin white shell. Although rare as a 

 beach shell, it is obtained by shrimp trawlers in fair numbers along the 

 Panama coast. 



Range — Lower California to Ecuador. Panama: Bella Vista; Panama 

 City. Panama Canal Zone: Thatcher's Ferry. Colombia: Cojimenes. 



Psammacoma siliqua (C. B. Adams) Plate 74, figures 9, 9a 



Tellina siliqua C. B. Adams, Ann. Lyceum Nat. Hist., New York, vol. 5, pp. 508, 546, 

 No. 470. — Turner, 1956, Occas. Papers on Mollusks, Mus. Comp. Zoo!., vol. 2, 

 No. 20, p. 85, pi. 19, figs. 15, 16. Panama. 



The shell is small, elongate, thin, convex, and strongly inequilateral, 

 the umbones and beaks placed near the posterior third, the anterior side 

 hence much longer, higher, inflated, widely rounded at the end, the posterior 

 side shorter, narrower, strongly flexed, and subtruncated at the end. The 

 left valve is a little larger than the right, rather strongly convex over all, 

 its dorsal and ventral margins straight and parallel, the left a little less 

 convex, flattened or impressed across the posterior-middle zone due to the 

 twist or bend of the valve towards the right. The outer surface is smooth 

 and shiny, marked only by the extremely minute lines of growth. Hinge 

 weak, the pallial sinus deep and reaching almost to the anterior adductor 

 scar, its lower limb about half confluent with the pallial line below. 



