PANAMIC-PACIFIC PELECYPODA 79 



Area lithodomus (Sowerby), Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 12, fig. 76. 

 Area (Litharea) lithodomus (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, No. 4, 



pp. 169, 170. — Rcinhart, 1935, Mus. royal d'Histoire nat. Belgique, Bull., tome 



11, No. 13, p. 18. Reinhart, 1943, Special Paper, Geol. Soc. America, No. 47, 



p. 27, pi. 11, figs. 1, 2, 3. 

 Litharea lithodomus (Sowerby), Frizzell, 1946, Jour. Paleont., vol. 20, No. 1, pp. 45-50, 



pi. 10, figs. 1-5; text figures 2, 6. 



There are four double-valve specimens in the British Museum (Nat. 

 Hist.) of which three have been placed apart in the type lot. These speci- 

 mens have the locality label of Monte Christi (the name of a town inland 

 from Manta). These specimens were apparently collected alive. The largest 

 specimen in the type lot measures 86.6 mm. 



Litharea lithodomus is fairly common at Manta, and loose valves can 

 generally be found along the beach to the west of the city. It appears to 

 be fairly well known to some of the fishermen who gather it along with the 

 larger Lithophagae, Chamas, and other mollusks for food and bait. Litharea 

 lithodomus is a true rock borer, the opening of its bore showing on the sur- 

 face of rocky ledges as a deep, rounded, or lens-shaped hole, often an 

 inch to an inch and a half across. At Manta, these bores are found princi- 

 pally on the under surface of projecting ledges of massive sandstones, avoid- 

 ing the softer layers. In cross-section, the bore is usually lenticular rather 

 than circular, its sides polished and tapering to a flat wedge at the end, the 

 mollusks being attached by its narrow, green byssus to one wall but loose 

 enough so that considerable movement backward and forward along the 

 bore is still possible. When feeding, the ark lies with its short posterior 

 end close to the open end of the bore but it pulls back quickly when 

 disturbed, its flattened, anterior end fitting snugly against the walls of the 

 bore but a narrow space above the umbones is open, often occupied by a 

 nestling Acar. This sliding movement along the bore results in heavy wear 

 of the sides and umbones of the shell which is thus often reduced to a paper 

 thinness, only small patches of the original bristly periostracum being re- 

 tained along the posterior side and along the ventral margin. 



Range — Panama southward to Santa Elena, Ecuador. Panama: Bucaro; 

 Burica Peninsula. Ecuador: Esmeraldas; Bahia; Manta; Manglaralto; Santa 

 Elena. 



Genus BARBATU Gray, 1847 



Type species by original designation and tautonomy. Area barbata Linne, 

 Recent, Mediterranean Sea. 



The shell is subquadrate to subelliptical in shape, subequivalve and in- 

 equilateral, the ventral margin straight or with a wide, open byssal gap or 

 notch, the posterior-umbonal slope rounded or angled. The cardinal area is 

 low or high, longer on the posterior side, covered by the ligament and with 

 obliquely transverse, sometimes tent-shaped grooves which begin under 

 the beak; the ligamental grooves may be developed on both sides of the 

 beak or only on the posterior portion; in the latter case, the anterior section 

 of the cardinal area is bare or covered only by an extension of the perio- 

 stracum. The sculpture is formed principally by small, close-set radial rib- 



