PANAMIC-PACIFIC PELECYPODA 369 



Amphidesma pulchra Sowerby, Reeve, 1853, Conch. Icon., vol. 8, Amphidesma, pi. 1, 



fig. 2. 

 Amphidesma striosum Turner, 1956, Occas. Papers on Mollusks, Mus. Comp. Zool., 



vol. 2, No. 20, p. 90, pi. 18, figs. 1, 2. (not A. striosum C. B. Adams). 

 Semele pulchra (Sowerby), Maxwell Smith, 19+4, Panamic Marine Shells, p. 62, fig. 



810.— Hertlein and Strong, 19+9, Zoologica, vol. 3+, pt. 4, No. 19, p. 2+6, pi. 1, 



fig. 15. 



Shell small or medium-sized, solid, ovate-elliptical, the beaks small, 

 trigonal and placed a little behind the middle, the anterior side hence longer 

 and narrower, its dorsal margin descending with both ends evenly and 

 broadly rounded. The posterior end is weakly flexed. The surface is sculp- 

 tured with fine, close, concentric riblets, sometimes a little oblique in the 

 middle zone; these concentrics are uniformly developed over the whole disk 

 except on the posterior slope where they are lacking while on the anterior 

 slope, the concentrics are cut through by a set of fine radial grooves. Escut- 

 cheon long, narrow, and flattened, the lunule smaller and deeply impressed, 

 both are generally colored a deep purple. Color white, cream or yellowish 

 gray, the interior white except the hinge and inner cavity which may be 

 blotched with purple. 



A specimen measures: Length 27.6 mm., height 23.1 mm., diameter 

 5.5 mm. 



Range — Nicaragua to northern Peru. Costa Rica: Puntarenas. Panama: 

 Bucaro. Panama Canal Zone: Palo Seco. Ecuador: Bahia de Caraques 

 (Cuming). Peru: Zorritos. 



Semele gnaymasensis Pilsbry and Low© Plate 65, figure 4; 



Plate 66, l.gure 6 



fiemele quaymasensis Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 

 84, p. 92, pi. 12, figs. 8, 9 "Guaymas". — Hertlein and Strong, 1949, Zoologica, 

 vol. 34, pt. 4, No. 19, pp. 243, 2+4. 



Shell irregularly ovate, nearly equilateral, compressed to slightly con- 

 vex; dorsal margin slightly convex behind, straight, and somewhat lower 

 in front of the beaks. Posterior-dorsal slope slightly depressed and flexuose, 

 its end somewhat squarely truncated, the posterior end well rounded. Sculp- 

 ture consists of strong, concentric, rounded ridges between slightly wider 

 interspaces, the concentrics often irregular and waved, especially over the 

 anterior slope where they are intersected by radial grooves, usually seven 

 in number, and in addition finely wrinkled by growth threads. The escut- 

 cheon is narrow and flat, marked with growth lines only, and often colored 

 a fine purple. The lunule is much smaller, depressed, an outside bordering 

 area wider. The pallial sinus is large and deep. The interior is white or cream- 

 colored, often with a staining of purple in the umbonal cavity. Surface is 

 usually colored with cream or buff, faintly mottled or rayed with purple, the 

 dorsal border and hinge teeth a deeper purple. 



A specimen measured, length 27.3 mm., height 22.7 mm., diameter 12.4 

 mm. Palo Seco, Panama Canal Zone. 



Another specimen, length 24.5 mm., height 18.7 mm. USNM 557879. 



Similar to S. venusta but shorter and with strong, radial grooves on 

 the anterior-dorsal margin, lacking or less strongly developed on the pos- 

 terior dorsal margin. The lunule and escutcheon are generally stained deep 

 purple. 



Range — Gulf of California to Panama. Mexico: Guaymas; Punta 

 Penasco. Panama Canal Zone: Palo Seco. 



