152 56 



species S. spathuliferus, Lam., which presents an almost incredible variability con- 

 cerning the colour-ornamentation, and the occurrence and arrangement of spines, 

 spatulate scales, etc.; but they may all be at once recognized by the characteristic 

 colours and appearance of the young valve which is insensible to other influences. 

 With such an example for consideration, I think it very probable that my supposi- 

 tion concerning the relationship between some of the East Indian forms, will prove 

 to be right. 



Spondylus Layardi, Reeve. 



Spondyliis Layardi, Reeve, Conchol. icon., IX, Spondylus, IS.'JH, Sp. Gfi. 



Strand of Koh Kahdat (Va). 

 Long. 27 mm., alt. 26 mm. 



Distribution:— Ceylon (Cuming), Gulf of Manaar (Thurston, Standen & 

 Leiceister). 



Plicatula imbricata, Menke. 



PUcahila imbricata, Mknke, Mollu.scor. Novae HoUandiae specini., 184,'!, p. 35, No. 196. 



— — — Hanley, Catalogue of recent bivalve shells, p. 288. 



— _ _- SowERBV, Tliesaurus Conchyl., I, p. 437, No. fi, pi. 90, fig. fi; pi. 91, figs. I,'') -18. 



— — — SowERBY in Reeve, Conchol. icon., XIX, 1874, Plicatida, Sp. 4. 



— chinensis, MoncH, Catal. conch, quæ reliq. Yoldi, II, 1853, p. 01, No. 761). 



Between Koh Rin and Cliff Rock, 15 fathoms (^/i). Koh Kram, 30 fathoms (1). 

 N. of Koh Kam, 5 fathoms, gravel (Va). Off Koh Kam, 10 fathoms, gravel (1). North 

 side of Koh Mesan, 10—15 fathoms, stones (1 -{- '^li). Between Koh Mesan and Cape 

 Liant, 5 — 9 fathoms (^l-i). Between Koh Mesan and Koh Chuen, 25—38 fathoms, 

 stones and shells (2). Koh Chuen, 10-30 fathoms (1 + 2/3). E. of Koh Chuen, 

 9—10 fathoms, shells (V2). S. of Koh Chuen, 30 fathoms, shells (1 + -Vs). Gulf of 

 Rayong, 7 — 10 fathoms, sand, mud, shells (-/a). North end of Koh Chang, 1 fathom, 

 old coral blocks (',2). Between Koh Kut and Koh Kahdat, 10 fathoms, shells (2). 



Long. 7 mm., alt. 8 mm. — long. 28 mm., alt. 33 mm. 



Distribution: — Singapore (Danish Exp. to Siam, and Sv. Gad), Andamans 

 (Melvill & Sykes), Aden (Shopland), Gulf of Tadjourah (Gravier, Anthony), He 

 Cameran, subfossil (Jousseaume), Mascarenes (v. Martens). — China (Hanley), 

 Philippines (Sowerby), Amboina? (Edg. Smith), Torres Strait (Melvill & Standen), 

 West Australia (Menke, Hanley), Port Jackson and Port Stephens (Angas), I'unafuli 

 Atoll? (Hedley). (Sowerby records it also from Honduras Bay). 



The species belonging to the genus Plicatula, owing to their great variability, 

 are exceedingly difficult to define and to characterize. Hence, numerous species 

 have been established which cannot be maintained and many erroneous determina- 

 tions have been made, which have resulted in the records of the geographical 

 distribution of the species frequently becoming quite misleading. Thus PI. spondy- 

 loidea, Meuscli. (= Pl.ramosa, Lam.),' has been recorded, e. g. from: Aden (Jousseaume), 



' PI. spondyloidea, Meusch. = PI. ramosa, Lam. = Barbadensis (Petiv.), d'Orb. = plicata, Chemn. 

 = cristala, Lam. = renifonnis, Lam. := gibbosa, (Lam.) Sow. ■— marginata. Say. 



