Shell to 120 mm. Inequilateral. Outline subrectangular to trigonal - subquadrate; small specimens usually subrectangular with short almost straight lateral margins, with slight dorsal auriculations; large specimens may remain subrectangular but in some the anterior area is small and acutely rounded, the posterior area is expanded with a long straight posterior margin. Dorsal area narrow, becoming deeply cleft. Ligament covering whole of dorsal area. Sculpture of narrow elevated riblets which are slightly nodulose, in trigonal forms the posterior area can be almost smooth. Periostraeum of dense dark brown lamellar bristles. Hinge line slight curved, teeth in a single series increasing in size laterally. Colour white. Habitat: Attached to rocks and corals.

Barbatia foliata (Forsskâl in Niebuhr, 1775) Leafy Ark Shell
10-90 mm. -» 'Leafy' lamellose pericostracum, coarse decussate sculpture. Shell white. Inhabits living hard corals and develops irregular shapes, some subtrigonal, some subrectangular. (90 mm)
Distribution: Common from Marsa Alam south, occasional in the Hurghada Reefs, South Sinai, and Dahab.
Notes: Easily confused with B. trapezina, but differs in having coarser and more knobby radial ribs. Spécimens with pericostracum are easily distinguished as B. foliata never has radial lines of spiny hairs.

For many years two forms were recognised, those ecomorphs which remained subrectangular being known as Barbatia lima Reeve and those becoming trigonal as B. foliata. To further complicate the situation discrimination between B. decussata and the form "lima" can be difficult. The two can be distinguished in the form of the periostracum, outline of lateral margins and sculptural details.

Indo-Pacific. Red Sea.