84 AXEL A. OLSSON 



This is a common species at Panama living under stones, B. tenera 

 (C. B. Adams), a Recent West Indian species and B. millifilia Dall, a 

 Pliocene fossil from Florida are both similar to the Pacific form. 



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

 City. Canal Zone: Palo Seco; Venado. Ecuador: Isia la Plata, Manta; 

 Puerto Callo; Santa Elena. Peru: Caleto Sal; Lobitos. 



Genus CALLOARCA Gray, 1857 



Type species by monotypy, Byssoarca alternate Sowerby. Recent, 

 Panama. 



Shell elongately subquadrate, relatively thin, with a strong, umbonal 

 angulation. Cardinal area as in Acar, the ligament nearly or wholly pos- 

 terior of the beak. Umbones and the middle of the valves with a shallow 

 sulcation. Sculpture is formed by fine, flattened riblets in raylike groups 

 on the anterior and middle surface but become much enlarged along the 

 umbonal angulation. 



Calloarea alteraata (Sowerby) Plate 4, figures 5, 5a 



Byssoarca alternata Sowerby, 1833, Proc. Zool. Soc. London, p. 17. 



Area alternata (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 13, fig. 88. 



Barbatia (Cucullarca) alternata (Sowerby), Maury, 1922, Paleont. Araer., vol. 1, No. 



4, p. 184, pi. 30, fig. 11. 

 Barbatia (Calloarea) alternata (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. 



America, No. 47, p. 30, pi. 11, figs. 5-7. — Durham, 1950, Mem. Geol. Soc 



America, No. 43, p. 55, pi. 1, fig. 14. — ^Rost, 1955, Allan Hancock Pacific 



Expeditions, vol. 20, No. 2, p. 186. 

 Area (Calloarea) alternata (Sowerby). Hertlein and Strong, 1943, Zoologica, vol. 28, 



pt. 3, No. 19, p. 159. 



This is an elegant species with the characters given above for the 

 subgenus. It is relatively common at Panama, particularly at Palo Seco, 

 Canal Zone, elsewhere it appears to be rare. Cuming's specimens were 

 dredged in 12 fathoms of water, attached to stones. West Colombia. Hert^ 

 lein and Strong recorded it from localities in Costa Rica, Nicaragua, and 

 the Gulf of California. It occurs as a Pleistocene fossil in Lower California. 

 The periostracum appears to have been thin, brown, membraneous, with 

 short, frondlike filaments, expanded at the end, set along the interspaces. 



Length 46.6 mm., height 24 mm., diameter 22 mm. 



Palo Seco, Canal Zone. 



Range — Gulf of California to Ecuador. Canal Zone: Palo Seco; Fort 

 Amador. Panama: San Carlos; Guanico. Ecuador: West Colombia (Cum- 

 ing). 



Genus ARCOPSIS von Koenen, 1885 



Type species by subsequent designation, Reinhart, 1935, Area limopsis 

 von Koenen. The type species is from the Paleocene of Denmark. 

 (Fossularca Cossmann, 1887). 



The shell is generally small, solid, plump, byssiferous, oblong to sub- 

 quadrate, subequilateral with high, full, subcentral umbones and prosogyrate 

 beaks, and nearly square, blunt ends. Hinge taxodont, the teeth interrupted 



