82 AXEL A. OLSSON 



Contour of specimens varies according to the conditions under which 

 they have grown. An average specimen has the following measurements: 

 length 80 mm., height 44 mm., diameter of closed valves 33 mm. 



Isla la Plata, Ecuador. 



Good figures of this species have been given by Maury and by Rein- 

 hart. The valves are often much distorted because of its nestling habit. 

 The varietal names of velataformis and lasperlensis were given by Sheldon 

 and Maury to such growth forms. Barbatia Candida (Gmelin) from Florida 

 waters is similar but usually smaller; larger specimens of B. Candida from 

 the north coast of Colombia are at times indistinguishable from the Pacific 

 shell. 



Range — Lower California to northern Peru and the Galapagos Islands. 

 Panama: Panama City; Pearl Islands; Bucaro. Colombia: Isla del Gallo. 

 Ecuador: Galeras; Cabo Pasados; Manta; Isla la Plata; Santa Elena. Peru: 

 Zorritos; Boca Pan; Caleto Sal; Lobitos. 



Genus ACAR Gray, 1857 



Type species by subsequent designation, Stoliczka, 1871, Area divari- 

 cata Sowerby. 



Shell a nestler, hence often variable in shape, from short subquadrate 

 to elongated pholadiform, the valves often distorted and usually with a solid 

 texture. The posterior side is the longer one, crossed obliquely by a sharply 

 angulated umbonal ridge. Sculpture is produced by fine or coarse, radial 

 riblets, beaded or cancellated by the concentrics, their edges of intersection 

 often sharply serrated. Periostracum is exceedingly thin, the color of the 

 whole shell white or cream. Hinge similar to Barbatia, the teeth numerous, 

 in a more or less continuous series, the distal teeth large and divergent. The 

 cardinal area is narrow, with the brown-colored ligament and ligamental 

 grooves restricted largely to the posterior portion, the remaining anterior 

 portion small, bare and white. The color of surface below the inconspicuous 

 periostracum is white. 



Acar gradata (Broderip and Sowerby) Plate 6, figures 6, 6a, Gb 



Area gradata Broderip and Sowerby, 1829, Zool. Jour., vol. 4, p. 365. — Gray, 1839, Zool. 



Beechey's Voyage, p. 152, pi. 43, fig. 1. — Reeve, 1844, Conch. Icon., vol. 2, 



Area, pi. 14, fig. 92. 

 Area (Acar) gradata (Broderip and Sowerby), Hertlein and Strong, 1943 Zoologica, 



vol. 28, pt. 3, p. 155. — Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist, 



vol. 107, art. 2, p. 174. 

 Area (Byssoarca) pholadiformis C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, 



vol. 5, pp. 484, 545, No. 419. (Not D'Orbigny, 1844). 

 Barbatia (Acar) gradata (Broderip and Sowerby), Maury, 1922, Paleont. Amer., vol. 



1, No. 4, pp. 180, 181, pi. 2, figs. 4, 6, 9.— Reinhart, 1939, Trans. San Diego Soc. 



Nat. Hist., vol. 9, No. 10, pp. 39-41, pi. 3, figs. 1, 2.— Reinhart, 1943, Special 



Paper, Geol. Soc. America., No. 47, p. 35, pi. 11, figs. 11, 12. 

 Acar gradata (Broderip and Sowerby), Bartsch, 1931, Proc. U. S. Nat. Museum, vol. 



80, art. 9, pp. 2, 3, pi. 1, five top figures. — Rost, 1955, Allan Hancock Pacific 



Expeditions, vol. 20, No. 2, pp. 189, 190, pi. 12, figs. 11, 12. 

 Acar panamensis Bartsch, 1931, op. cit., pp. 3, 4, pi. 1, five bottom figures. 

 Barbatia (Acar) rostae S. S. Berry, 1954, Leaflets of Malacology, No. 1, No. 12. 



The shell is small to medium-sized (length 33 mm.), oblong, subrhom- 

 boidal to quite elongated, often much distorted and frequently showing 

 worn spots along the sides caused by abrasion against the wall of the 



