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, ete.; 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. 
Spondylus Layardi, Rerve, Conchol. icon., IX, Spondylus, 1856, Sp. 66. 
Strand of Koh Kahdat ('/2). 
Long. 27 mm., allt. 26 mm. 
Distribution: — Ceylon (Cumine), Gulf of Manaar (THurston, STANDEN & 
LEICEISTER). 
Plicatula imbricata, Menke. 
Plicatula imbricata, Menke, Molluscor. Novae Hollandiae specim., 1843, p. 35, No. 196. 
— _ = Haney, Catalogue of recent bivalve shells, p. 288. 
— = -- Sowersy, Thesaurus Conchyl., I, p. 437, No. 6, pl. 90, fig. 6; pl. 91, figs. 15 —18. 
— — — Sowersy in Reeve, Conchol. icon., XIX, 1874, Plicatula, Sp. 4. 
— chinensis, Moncu, Catal. conch. que relig. Yoldi, II, 1853, p. 61, No. 766, 
Between Koh Rin and Cliff Rock, 15 fathoms (7/2). Koh Kram, 30 fathoms (1). 
N. of Koh Kam, 5 fathoms, gravel (‘/2). Off Koh Kam, 10 fathoms, gravel (1). North 
side of Koh Mesan, 10—15 fathoms, stones (1 + */2). Between Koh Mesan and Cape 
Liant, 5—9 fathoms (7/2). Between Koh Mesan and Koh Chuen, 25—38 fathoms, 
stones and shells (2). Koh Chuen, 10—30 fathoms (1 + 7/2). E. of Koh Chuen, 
9—10 fathoms, shells (‘/2). S. of Koh Chuen, 30 fathoms, shells (1 + */2). Gulf of 
Rayong, 7—10 fathoms, sand, mud, shells (7/2). 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 Sy. Gap), Andamans 
(MeLvitt & Sykes), Aden (SHOPLAND), Gulf of Tadjourah (GravieR, ANTHONY), Ile 
Cameran, subfossil (JOuSSEAUME), Mascarenes (v. MARTENS). — China (HANLEy), 
Philippines (SowEerBy), Amboina? (Epc. Smirn), Torres Strait (MELvILL & STANDEN), 
West Australia (MENKE, HANLEy), Port Jackson and Port Stephens (ANGas), Funafuti 
Atoll? (HepLey). (Sowersy records it also from Honduras Bay). 
The species belonging to the genus Plicafula, 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 Pl. spondy- 
loidea, Meusch. (= Pl. ramosa, Lam.),! has been recorded, e. g. from: Aden (JOUSSEAUME), 
1 Pl. spondyloidea, Meusch. = Pl. ramosa, Lam. = Barbadensis (Petiv.), d’Orb. = plicata, Chemn. 
= crisltala, Lam. = reniformis, Lam. = gibbosa, (Lam.) Sow. = marginala, Say. 
° 
