19 115 
Long. 24 mm., alt. 14 mm., crass. 10 mm. 
Between Koh Rin and Cliff Rock, 15 fathoms (*/2). Koh Kram, 30 fathoms ('/2). 
Gulf of Koh Chang, 3—5 fathoms, soft clay (7/2). Between Koh Kut and Koh Kahdat, 
10 fathoms, shells (°/2). 
This characteristic species is nearest related to A. obliquata, Gray, and A. 
decussata, Lischke, but may easily be distinguished from these forms. 
Arca (Fossularca) pectunculiformis, Dunk. 
Barbatia peclunculiformis, DuNKER, Novitates conchologicae, 1866, p. 88, pl. 28, figs. 4—6. 
Arca (Barbatia) peclunculiformis, DuNker, Martini u. CHEMNITZ, Conchyl. Cabin., VII, 2 Abth., p. 125, 
pl. 32, figs. 5—6. 
—  (Noetia) — -- Lamy, Journ. de Conchyl., vol. 55, 1907, p. 300. 
W. of Koh Chuen, soft clay and mud ('*/2). S. of Koh Samit, 20 fathoms, 
mud (‘/2). Gulf of Koh Chang, 5 fathoms, soft clay (‘/2). Strand of Koh Kahdat 
(1/2). S. of Koh Kahdat, 8—10 fathoms, mud (?/2). Between Koh Kahdat and Koh 
Kut, 6 fathoms, clay mixed with sand (!*/2). S. of Koh Kut, 17—20 fathoms, mud ('/:). 
W. of Koh Kut, 15 fathoms, mud (‘/2). W. of Koh Kong (1). 
Long. 3—10 mm. 
Distribution: — Karikal (Coromandel Coast, subfossil, DAuTZENBERG), Borneo 
(DunKER), Surahaja (Java, Ep. v. MARTENS). ! 
Arca olivacea, Reeve, is very closely related to this species. Can some of the 
recorded occurrences of A. lactea L. in Asiatic and Australian waters, be due to 
erroneous determination of A. pectunculiformis, Dunk.? 
Arca (Fossularca) sculptilis, Reeve. 
Arca sculptilis, REEVE, Proc. Zool. Soc. London, 1844, p. 128. — Conchol. icon., H, 1844, Arca, Sp. 118. 
— (Barbatia) sculptilis, Rezve, Eva. SMirn. Rep. Lamellibranchiata of the Challenger Exped., p. 262. 
— (Acar) = — KoseL_r in Martini u. CHemnirz, Conchyl. Cabin., VIII, 2 Abth, p. 193, 
No. 175, pl. 46, fig. 14. 
Common between Koh Lan and Koh Mak, many specimens in 1—88 fathoms, 
sand, mud, gravel and shells. 
Long. 2—13 mm. 
Distribution: — Bombay (MEtvitt & ABERCROMBIE, A. Zebuensis, REEVE), 
Karachi (MELvILL & STanpEN). — Amboina (Challenger), Philippines (REEVE), Torres 
Strait. (MELvILL & STANDEN). 
Lamy (Journ. de Conchyl., vol. 55, 1907, p. 100) identifies A. sculptilis, REEVE, 
with A. afra, Gmel. var. solida, Sow. I do not think that he is correct in so 
doing. Apart from other considerations the differing geographical distributions 
of A. afra, Gmel. (= A. pisolina, Lam.), A. solida, Sow., and A. sculptilis, Reeve, are 
at once conspicuous; besides, it seems to me that A. sculptilis may very well be 
1 As communicated by letter. 
