1917- -^^'c^ ivibricata var. arabica Lamy, Bull. Mus. d'Hist. Nat. Paris, XXIII, p. 26. 

 1917. Arca imbricata var. avellayia Odhner, Kungl. Sv. Akad. Handl., LII (N" 16), p. 21. 

 1919. Arca imbricata var. avellana Odhner, Ark. Zoôl., XII, N*' 61, p. 8. 

 1926. Arca imbricata Pallary, Mém. Inst. Egypte, XI, p. 114, pi. XIV. 



1929. Arca imbricata vars. arabica and avellana Dautzenberg, Faun. Colon. Français., III, 

 PP- 573. 574, 



After a careful examination of the collections in the British Muséum (Nat. Hist.), London, 

 the "Siboga" collection and the literature on the subject I hâve corne to the conclusion that 

 West Indian species to which the name A. imbricata Bruguière may be applied is certainly 

 distinct from the Indo-Pacific form. The Indo-Pacific form, as the synonymy given above shows, 

 has been given varions names by the différent authors, and I hâve out of thèse selected the 

 oldest name, A. avellana Lamarck, for the species. My conclusions in gênerai agrée with Lamy 

 (loc. cit.), but I differ from him regarding the Indo-Pacific form being only a variety of the 

 West Indian species. Further the two forms arabica and avellana cannot be distinguished from 

 one another and I hâve, therefore, included the former in the synonymy of the latter. Probably 

 A. martensi Dunker ^) is also a form of this species, but I hâve not been able to get together 

 sufficient material to settle this question. 



Distribution : — A. avellana is widely distributed in the Indo-Pacific area. It has been 

 recorded from the Gulf of Suez and the Red Sea, to S. x'\frica, from the Mascarenes through 

 the Gulf of Manaar, Mergui Archipelago, the Philippines and New Caledonia to Australia and 

 as far north as Japan. 



In the "Siboga" collections A. avellana is represented by spécimens from the Bay of 

 Badjo, . West Coast of Flores (St. 50), Bay of Nangamessi, Sumba (St. 53), Anchorage off 

 Dongala, Palos Bay, Celebes (St. 86), Anchorage off Sawan, Siau Island (St. 125), Anchorage 

 off Lirung, Salibabu Island (St. 133), Anchorage off Laiwui, Coast of Obi Major (St. 142), 

 Wunoh Bay, N. W. coast of Waigeu Island (St. 152), St. 225 (5700 m. N., 279° E. from South 

 point of South Lucipara Island) and Tuai Anchorage, Kei Islands (St. 258). Ail the spécimens 

 in the "Siboga" collection are of a small size, the largest being 33 mm. long X i7-5 irim. high X 

 22.8 mm. maximum diameter. 



2. Arca iJVavicnla) veîttricosa Lamarck. 



1705. Pecten saxatilis Rumph, Amboin. Rariteitk., p. 143, pi. XLIV, fig. L. 



1767. Pecten saxatilis Petiver, Anim. Amboin, p. 4, pi. XVII, fig. 6. 



1819. Arca ventricosa Lamarck, Anim. sans Verteb., VI, p. 38. 



1833. Byssoarca truncata Sowerby, Proc. Zool. Soc. London, p. 19. 



1835. Arca ventricosa Deshayes in Lamarck, Anim. sans. Verteb., VI, p. 463, 



1843. Arca ventricosa Hanley, Rec. Biv. Shells, p. 153. 



1844. Arca zébra and A. truncata Reeve, Conch. Icon., II, Arca, pi. XI, figs. 69, 74. 



1845. Arca truncata and A. zébra Catlow & Reeve, Conch. Nomencl. p. 51. 



1847. Arca ventricosa Philippi, Abbild. Beschreib. Conch., II, p. 211, Arca, pi. III, figs. 4, 5. 



1848. Arca {Byssoarca) truncata and A. ventricosa, Nyst, Mém. Acad. Roy. Belgique, XXII, 



pp. 74, J6. 

 1858. Arca {Byssoarca) zébra Fischer, P. (non Sowerby), Journ. Conchyliol., VII, p. 339. 



i) Dunker, W. B. R. H. — Novitat. Conch., Moll. Mar. p. m, pi. XXXVII, figs. 17, 18 (1870). 



SIBOGA-EXPEDITIE LIIIC. 



