129 225 



Eastonia (Merope) Nicobarica, Gmel. 



Mactra niqosa Indiae orientalis, Chkmmtz, Coiicliyl. Cabin., VI, 1782, p. 238, pi. 24, fig. 237. 



nicobarica, Gmelin, Syst. Nat. ed. XIII, 1790, p. 3261, No. 24. 

 Anaiinella Nicobarica, Gmelin, Tennant, Natural History of Ceylon, 1861, p. 389. 



Ltilrcirid Merope) Nicobarica, Gmelin, v. Martens, Journ. Linnean Society, Zoology, 1887, vol.21, p. 217, 

 pi. 16, fig. 7. 

 — — nicobarica, Gmelin, Thuhston, Ràmésvaram Island and Fauna of the Gulf of Manaar, 



2 ed., 1895, p. 128. 

 Mactra Aegyptiaca, Chemnitz, Conchyl. Cabin., XI, 1795, p. 218, pi. 200, figs. 1955— 56. 

 Luiraria Eçjtjptiaca, Gray, Hanley, Catalogue of rec. biv. shells, p. 26, pi. 6, fig. 34. 

 Mactra Ægyptiaca, Chemnitz, Reeve, Conchol. icon., VIII, 1854, Mactra, Sp. 112. 

 Lutraria Aegiptiaca, — Issel, Malacologia d. Mar Rosso, 1869, p. 52. 



Merope Ægyptiaca, Gray-, Axgas, Proc. Zool. Soc. London, 1871, p. 100. 



Aegyptiaca, Chemnitz, Dunker, Index inolluscor. mar. Japon., 1882, p. 184. 

 Mactra [Merope ægyptiaca, Chemnitz, Edg. Smith, Proc. Zool. Soc. London, 1891, p. 428, No. 222. 

 Eastonia — aegyptiaca, — Pilsbry, Marine Mollusks of Japan, 1895, p. 120. 



Standella Ægyptiaca, Chemnitz, Shopland, Proc. Malacol. Soc. London, V, p. 177. 

 Mactra reticulata, Spengler, Skrivter af Naturhistorie Selskabet, V Bd., 2 Hefte, 1802, p. 119. 

 Lutraria Cheninitzii, Philippi, Zeitschr. f. Malakozool., 1849, p. 26, No. 99. 



Between Koh Riot and Koh Mesan, 3 — 5 fathoms, sand ('/a). Koh Kahdat, 1 

 fathom, sand ('/l'). 



Long. 18 — 43 mm. 



Distribution: — Singapore (shallow water, Sv. Gad), Mergui Archip., Nico- 

 bars, Ceylon, Karachi, Aden, Red Sea (Chemnitz, Issel, Forskål (Mus. Univ. Hafn.), 

 Sturany). — Java, Panay Isl. (Mus. Univ. Hafn.), Japan, Liukiu Isis., Lake Mac- 

 quarie (New South Wales). 



As the original specimens of Chemnitz's "Mactra rugosa Indiae orientalis" and 

 Mactra Aegyptiaca have been at my disposal, it has been possible for me to verify 

 the reciprocal relation of these forms. Mactra rugosa Indiae orientalis has been 

 described by Chemnitz from a specimen in Spenüler's collection, and was after- 

 wards named Mactra reticulata by the latter. The figure given by Chemnitz is very 

 bad, but Reeve's figure, Sp. 112, is an excellent illustration of the species, both as 

 regards its form and its sculpture; the reticulata-îorm thus indicates the individuals 

 with pointed posterior end and coarser radiating ribs, and the interstices between 

 the ribs 2 — 3 times the width of the ribs. The other species M. Aegyptiaca has 

 been figured fairly well by Chemnitz ; it comprises the forms with oval shells, and 

 finer, more closely set radiating ribs; but between these two extremes there is an 

 extensive series of intermediate forms, which I have before me, and which distinctly 

 show that it is same species which varies. I have also at hand that small characteristic 

 form which Ed. v. Martens describes and figures from "King Island, mud-bank ex- 

 posed at spring-tide;" my specimen was taken at Singapore in shallow water, it is 

 only a thin-valved, littoral, local form of E. Nicobarica Gm., ornamented with rather 

 slight and delicate ribs. 



1). K. I). ViilcnsU. Sclsk. .Skr., 7. Ilielilie. n:iliir\ i<k>nsk. i)|; miithem. AW. V. 3. 29 



