Arca avellana: Testa oblonga, crassa, costis numerosis angustis nodulosis instructa, antice truncata, postice elongata, acuminata, valde concava, et curvatim biangulata, inferne haud hians; umbones remoti, incurvati, prominentes, ligamenti area lata, leviter concava ; ligamentum fuscum, sulcis paucis sculptum. Long. 19, lat. 9, crass. 13 mm.
This species is remarkable for the concavity below the dorsal margin, throwing into prominence two rounded angles or keels.

Arca avellana: Shell to 40 mm. Inequilateral, beaks towards the anterior. Outline irregular, subtrapezoidal: anterior and ventral margins rounded, sinuous; byssal gape large; posterior carina well developed; posterior margin straight. Sculpture of 4-6 riblets on the posterior area elsewhere finely decussate. Ligament covering whole of dorsal area. Periostracum usually lost except on posterior carina where stiff, serrate, spathulate bristles persist. Inner margin serrate except on posterior margin where crenulate. Colour, buff on anterior area darker shades of brown on posterior area.

Arca avellana: Area avellana Lamarck, 1819
15-62 mm. —» At least one oblique ligament mark can be found posterior to the triangle of marks under the beaks. Ligament itself covers entire dorsal area. Anterior white or at least lighter than the brown posterior. (41 mm)
Distribution: Common in the Gulf of Suez. Occasional in the far south.

Arca avellana: Arca avellana is closely allied to A. ventricosa but can be distinguished on the characters of the dorsal area. A. avellana has usually been known under the name of A. imbricata Bruguiere but that species is Caribbean in distribution (Lamy 1917).

Arca avellana: Throughout the Red Sea. Indo-Pacific.