364 AXEL A. OLSSON 



of the valves stained with brown, yellow or purple. The valves are nearly 

 equal in size, equilateral, the small beaks placed near the middle. Surface 

 smooth but on close inspection seen to be covered with fine, widely spaced, 

 ■concentric threads, best developed on the sides and near the ventral margin, 

 often worn off the umbones: there is also a submicroscopic sculpture of 

 radial striae which on the anterior and posterior slopes assume a fan- 

 shaped pattern. 



Length 24.7 mm., height 21.1 mm., diameter 11.6 mm. Santa Elena, 

 Ecuador. 



Shells from Panama are more circular than the typical form from 

 Ecuador but are otherwise quite similar. The type of C. B. Adams, A. 

 striosum seems to be lost; the specimen figured by Turner as the type is 

 evidently a misplaced shell: this specimen was seen by the author some 

 years ago and identified then as S. pulchra. 



This small Semele is especially common along the Ecuadorian coast, 

 and except for its much smaller size, it shares many characters in common 

 with S. pTojicua (Pulteney) of the Western Atlantic. 



Range — Panama southward to Peru. Panama: Panama City; Bucaro. 

 Panama Canal Zone: Venado Beach. Ecuador: Esmeraldas; Manta; Puerto 

 Callo; Santa Elena. Peru: Zorritos; Boca Pan; Negritos. 



Semele pallida (Sowerby) Plate 66, figure 8 



Amphidesma pallidum Sowerby, 1833, Proc. Zool. Soc. London for 1832, p. 199 Salango. 



—Sowerby, 1833, Conch. Illust., No. 3, pi. 17, fig. 3. 

 Amphidesma pallida Sowerby, Reeve, 1853, Conch. Icon., vol. 8, Amphidesma pi. 4, 



fig. 22. 

 Semele regularis Dall, 1915, Proc. Acad. Nat. Sci. Philadelphia, vol. 67, p. 25 off La 



Paz, Lower California. 

 Semele simplicissima Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, vol. 



84, p. 93, pi. 12, figs. 6, 6a Acapuico. — Hertlein and Strong, 1949, Zoologica, 



vol. 34, pt. 4, p. 247. 

 Semele paziana Hertlein and Strong, 1949, op. cit., p. 274. (New name for S. regularis 



Dall, 1915, not S. regularis E. A. Smith, 1885). 



Shell ovate, thin, delicate, moderately convex, slightly inequilateral, 

 the beaks being placed not quite median, the anterior side being a little 

 longer and narrower, its dorsal margin sloping and nearly straight, rounded 

 at the end. Posterior side is a little higher, depressed or flattened, setoff 

 by a weak angle from the rest of the surface, its end appearing truncated 

 and straight. Sculpture consists of fine, narrowly shelving concentrics, their 

 interspaces narrow and flat, smooth or without concentric lineation. Color 

 usually a dingy white, the interior of fresh specimens tinted with salmon 

 pink, orange or purple. Average length about 25 mm. 



There seems to be little doubt that Semele -pallida, regularis, and 

 simplicissima represent a single species characterized by its ovate form, 

 thin shell, and fine concentric sculpture. The fine, concentric lines between 

 the riblets (as described for S. regularis) ^ are not well developed on all speci- 

 mens but can generally be seen on close inspection. 



Range — Lower California to Ecuador. Mexico: Off La Paz (Dall for 

 regularis); Acapuico (Pilsbry and Lowe for S. simplicissima). Ecuador: 

 Esmeraldas; Salango (pallida). 



