262 166 



Hemicardittm (Ctenocardium) fornicatum, Sowerby, Melvim. & Standen, Proc. Zool. Soc. London, 1906, 



p. 840. 

 Cardium Adamsii, Reeve, Voyage of "Samarang," p. 77, pi. 22, fig. 2. 



— Virgo, Reeve, Concho), icon., 1845, II, Cardium, Sp. 120. 



Commonly distributed from the Gulf of Rayong and Cape Liant to Koh Kut, 

 1—15 fathoms, sand, mud, and gravel (26). 



Long. 6—26 mm. 



Distribution: — Andamans (Edg. Smith), S. Nilandu and N. Male Atoll (Edg. 

 Smith), Persian Gulf (Melvill & Standen), Red Sea (Sturany), Providence Isl., 

 Mascarenes ("Alert"). — Borneo ("Samarang"), Tizard Bank, southern China Sea 

 (Edg. Smith), Tonga Isis. ("Challenger"). 



The present species is often difficult to distinguish from Hemicardium imbri- 

 catum, Sow. The number of the ribs is variable; the intercostal sculpture (at 

 any rate in the material before me) is the same in both the species. Sowerby 

 says regarding fornicalam that the ribs are set with "vaulted imbrications," while 

 Edg. Smith ' states regarding the same species that they are ornamented with "short 

 hollow spines." In younger and well-preserved specimens these "spines" may be 

 as well-developed as in imbricatum. The specimens from the Gulf of Siam are 

 quite white on the outer side of the valves and precisely resemble Card, virgo, 

 Reeve, which is synonymous with C. fornicatum, Sow. 



Hemicardium (Ctenocardium) imbricatum, Sow. 



Cardium imbricatum, Sowerby, Proc. Zool. Soc. London, 1840, p. 110. 



— — — Conchol. Illustr., Sp. 85, fig. 48. 



— — — Reeve, Conchol. icon., II, Cardium, Sp. 28. 



Several (22) specimens taken at Koh Chang, Koh Mak, Koh Kahdat, Koh Kut, 

 Koh Samit and several places in 5—30 fathoms, mud, gravel, and clay mixed 

 with sand. 



Long. 6 — 27 mm. 



Distribution:— Torres Strait (Murray Isl.), off Cape York (North AustraHa), 

 West Australia (Swan River). 



Card, hystrix, Reeve, from the Philippines and the Andamans, with strongly 

 developed spines, approaches somewhat Card, imbricatum, Sow. 



Fam. Tridacnidae. 



Tridacna squamosa, Lam. 



Tridacna squamosa, Lamarck, Hist. nat. d. anim. s. vert., VI, 1 p. 1819, p. 106. — éd. 2, VII, 1836, p. 10. 



— - — QuoY et Gaimard, Voyage de l'Astrolabe, H, 1833, p. 487, pi. 79, fig. 1. 



— — — Martini u. Chemnitz, Conchyl. Cabin., VIII, 4 Abth., p. 5, pi. 1, figs. 1—3; 



pi. 2, figs. 1—2. 



' Report on the Lamellibranchiata of the Challenger Expedition, p. 164. 



