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Show 1S94.] LAND-SHELLS FROM THE SAMUI ISLANDS. 153 Operculum cyathiforme, subtestaceum, intus profundissime cglin-drico- excavatum, lave, nitens, extus breviter cylindricum, turn semiglobosum, apice subplano, anfr. 12 marginibus lamellatim elevatis, in interstitiis oblique striati. Diam. maj. 24-5, min. 18, alt. 13-5; operculi diam. 6, alt. 4 millim. This very interesting form differs from all known species of Rhiostoma in the want of a sutural tube, whilst the operculum is quite typical. This is another proof that the formation of a tube, which is but an extreme development of the " wing" at the peristome of Eucyclotus and Pterocyclus, is of less systematic value than is generally supposed. The classification of operculate shells will have ultimately to rely upon the structure of the operculum chiefly, if not exclusively. 24. CYCLOPHORUS MALAYANUS, Bens. Whilst Prof, von Martens is quite right in combining the so-called C. malayanus of the ' Conchologia Indica' and of Reeve with the very variable C. aurantiacus, Schum. (Journ. Linn. Soc, Zool. xxi. 1887, p. 159), I believe with him that the true C. malayanus, Bens., of Pulo Penang is a distinct species. A fine large Cyclophorus of the Samui group I consider to belong to it, although I cannot compare typical specimens. M y largest example measures 48 by 39 millim. 25. CYCLOPHORUS DIPLOCHILUS, sp. nov. (Plate XVI. fig. 24.) T. pro genere anguste umbilicata, subdepresse turbinata, solicla, transverse leviter striatula, lineis spiralibus rugulosis decussata, pallide corneo-fusca, tceniis interruptis castaneis, interdum strigis castaneis fiammulatis picta. Anfr. 4|, perconvexi, ad suturam subplanati ; ultimus antice vix descendens. Apertura sat obliqua, circularis ; peristoma duplex, externum album, late expansum, revolutum, marginibus callo junctis, columellari dila-tato ; internum aureum aut aurantiacum,valde nitens, continuum, late expansum, margine dextro valde dilatato, crassum, quasi multiplicatum, sulco ah externo separatum. Operculum normale. Diam. maj. 38, min. 28, alt. 31 ; diam. apert. c. perist. 24, intus 14 millim. Forma minor : diam. maj. 30, min. 22-5, alt. 25; diam. apert. 18, intus 11 millim. At first I believed this fine shell to be C. cucullatus, Gld., of Mergui, of which no figure has been published, and which v. Martens in his able paper on the Mergui Archipelago does not mention. According to the diagnosis of Gould's species as given by Pfeiffer (Hon. Pneum. suppl. i. p. 44), however, there appear to exist sufficient differences to justify the separation of the two forms specifically. C. cucullatus is considerably smaller, white, the last whorl subangulate, the columellar margin not dilatate, the outer peristome is only called " reflexiusculum," whilst in my species it is strongly recurved, &c. Otherwise the formation of |