27 123 
Koh Chuen, 30 fathoms (1). Between Koh Kut and Koh Kahdat, 10 fathoms, 
shells ('/2). S. of Koh Kahdat, 8—10 fathoms, mud (°/2). 
Long. 4--15 mm. 
Distribution: — Ceylon (HAN LEy), Mascat (Brit. Mus.), Red Sea (fossil, IssEt). 
— China (Collect. de V’Ecole d. Mines, Paris). 
All the specimens from the Gulf of Siam are small, but correspond well with 
REEVE’s diagnosis; the valves are thin; in the specimens without an epidermis there 
is a distinct intercostal-sculpture between the 46 radiating ribs; the angular transi- 
tion, mentioned as occurring between the hinder and lower margins, is more 
rounded than is shown in ReeEve’s figure; the characteristic groove upon the 
umbones is very pronounced in quite small specimens. 
Arca (Scapharca) crebricostata, Reeve. 
Arca crebricostala, Reeve, Proc. Zool. Soc. London, XII, 1844, p. 46. 
— — —- Conchol. icon., I, Arca, Sp. 61. 
= = = Crosse et Fiscuer, Journ. de Conchyl., vol. 87, 1889, p. 292. 
— (Scapharca) crebricostala, Reeve, Martini u. CaEMNitz, Conchyl. Cabin., VIII, 2 Abth., p. 91, pl. 25, 
figs. 3—4. 
— (Anadara _— —  P. Fiscuer, Catal. d. Moll. de l'Indo-Chine, p. 216. 
— — — — Lamy, Journ. de Conchyl., vol. 55, 1907, p. 253. 
Koh Mak, sand coast (°/2). On the coast of Koh Kahdat (°/2). 
Long. 29—49 mm. 
Distribution: — Cochin China, Annam. 
I cannot make the great number of ribs (483—44), stated by Reeve and Kosetr, 
agree with the figures given by the same authors, which apparently show only 
about 35—387. Neither are so many ribs found in the specimens from the Gulf of 
Siam (in which there are only about 35), unless the most anterior, duplicate ribs 
are to be counted twice. 
Arca (Scapharca) clathrata, Reeve. 
Arca clathrala, Reeve, Proc. Zool. Soc. London, XII, 1844, p. 44. 
-— —  Conchol. icon., II, Arca, Sp. 48. 
— (Anomatlocardia) clathrata, Reeve, MArrint u. CHEMNITZ, Conchyl. Cabin., VII, 2 Abth., p. 179, pl. 
44, fig. 5. 
— (Scapharca — _ Epa. A. Smiru, Rep. Challenger Lamellibranchiata, p. 266. 
— (Anadara) — — Lamy, Bull. du Mus. d’Hist. Nat. Paris, 1904, p. 277. 
= = — Journ. de Conchyl., vol. 55, 1907, p. 229. 
Scapharca pygmea, H. AvAms, Proc. Zool. Soc. London, 1872, p. 11, pl. 3, fig. 15. 
Arca — ~ Cooke, Ann. and Mag. of Nat. Hist., 5 Ser., vol. 18, 1886, p. 94, 
Common between Koh Lan and Koh Kut, many specimens in 1—30 fathoms, 
mud, sand, clay, and shells. 
Long. 3—33 mm. 
Distribution:— Madras, Felidu Atoll (Maldive Archip.), Gulf of Oman 
(MeLvitL & STANDEN), Gulf of Aden, Red Sea, Suez. — Philippines, Amboina, Torres 
Strait, Mast Head Reef (Queensland). 
16° 
