PANAMIC-PACIFIC PELECYPODA 373 



Range — Panama to Ecuador. Panama: Panama (C. B. Adams). Colom- 

 bia: Isla del Gallo. Ecuador: Jaramijo. 



Genus ABRA Lamarck, 1818 

 Type species by monotypy, Mactra tenuis Montagu. Recent, European 

 Seas. 



Shell small or of medium size, generally subtriangular to subquadrate, 

 the posterior end narrower and shorter, often weakly flexed at the end, 

 the valves moderately convex. Surface sculptured principally with growth 

 lines. External ligament narrow, attached along the upper surface of a 

 small, nymphal ridge which separates it from the larger, elongated internal 

 chondrophore Ijing along the posterior side of the hinge plate. Hinge arma- 

 ture weak; the right valve has two cardinal teeth and generally two, lateral 

 laminae; the left valve has a single, strong, cardinal tooth and traces of a 

 second, the lateral teeth weak or absent. The pallial sinus is large, widely 

 confluent with the pallial line below. 



In this genus, the hinge is like that of Semele but with smaller cardinal 

 teeth, sometimes much reduced or vestigial. Valves are generally inequi- 

 lateral, the anterior side generally well rounded. Surface smooth or with 

 fine, concentric growth lines and covered with a thin periostracum, silky or 

 faintly iridescent. 



Abra tepoeana Dall 



Abra tepoeana Dall, 1915, Proc. Acad. Nat. Sci. Philadelphia, vol. 67, p. 28. 



Abra palmeri Dall, 1915, op. cit., vol. 67, p. 28. Ballenas Lagoon on the west coast of 

 Lower California; Panama Bay, tlie type locality. — Hertlein and Strong, 1949, 

 Zoologica, vol. 34, pt. 4, No. 19, p. 250, pi. 1, figs. 16, 18, 20, 23. 



Shell small or of medium size, short, high, moderately convex. Anterior 

 side longer, rounded at the end, the posterior side shorter, its dorsal margin 

 descending more rapidly into a rounded end. The valves are thin, dehcate, 

 subequal, white, the surface marked with fine growth lines. Pallial sinus 

 large, deep, reaching beyond the middle of the cavity, rounded, widely con- 

 fluent with the pallial line below. My largest specimen about 12 mm. 



This species is the Pacific analogue of the West Atlantic A. lioica Dall. 

 The name "A. palmeri Dall" was apparently given to the mature form. 



Range — Gulf of California to northern Peru. Panama: Biicaro. Panama 

 Canal Zone: Venado Beach. Ecuador: Santa Elena; Ancon. Peru: Tumbez; 

 Zorritos. 



Abra paeifica Dall 



Abra paeifica Dall, 1915, Proc. Acad. Nat. Sci. Philadelphia, vol. 67, p. 28 "Guaymas, 

 Mexico." 



Shell small, thin, white, finely concentrically sculptured, giving to the 

 surface a silky look; the concentric lines slightly prominent on the dorsal 

 side of the posterior side. Beaks not prominent, slightly anterior; outline 

 elongate^ attenuated and pointed behind, rounded in front; with only faint 

 traces of radial striae or none. Hinge normal, right cardinal tooth bifid, 

 anterior right laterals stout, very short, posterior feeble, longer; left valve 

 with a bifid cardinal and no laterals. Pallial sinus obscure. 



Length 9 mm., height 5.5 mm., diameter 3.0 mm. (Dall, 1915.) 



