1894.] LAND-SHELLS EROU THE SAMUI ISLANDS. 153 



Operculum cgathiforme, subtestaceum, intus profundissime ci/lin- 

 drico-excavatum, lave, nitens, ecctus breviter cylindricum, turn 

 semiglobosum, apice subplano, anfr. 12 marginibus lamellatim 

 elevatis, in interstitiis oblique striati. 

 Diam. maj. 24*5, min. 18, alt. 13*5 ; opermli 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 peri- 

 stome of Eucyclotus and Pterocydus, 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 malayantts, Bens. 



AVhilst Prof, von Martens is quite right in combining the so- 

 called C. malayanus of the ' Couchologia Indica ' and of Reeve with 

 the very variable G. aurantiacus, Schum. (Journ. Linn. Soc, Zool. 

 xxi. 1887, p. 159), I believe with him that the true G. malayanus, 

 Bens., of Pulo Penang is a distinct species. A fine large Cyclo- 

 phorus of the Samui group I consider to belong to it, although I 

 cannot compare typical specimens. My largest example measures 

 48 by 39 millim. 



25. Cyclophorus diplochilus, sp. nov. (Plate XVI. fig. 24.) 



T. pro genere anguste umbilicata, subdep>resse turbinata, solida, 

 transverse leviter striatula, lineis sjpiralibus rugulosis decussata, 

 jiallide corneo-fusca, tceniis interruptis castaneis, interdum 

 strigis castaneis flammulatis picta. Anfr. 4|, perconvexi, ad 

 suturam subplanati ; idtimus antice vix descendens. A'pertura 

 sat obliqua, circidaris ; 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 nonnale. 

 Diam. maj. 38, min. 28, alt. 31 ; diam. apert. c. perist. 24, intus 



14 millim. 

 Porina minor : diam. maj. 30, min. 22'5, alt. 25 ; diam. apert. 18, 



intus 11 millim. 

 At first I believed this fine shell to be G. cumllatus, Gld., of 

 Mergui, of which no figure has been published, and which v. Mar- 

 tens in his able paper on the Mergui Archipelago does not 

 mention. According to the diagnosis of Gould's species as given 

 by Pfeiffer (Mon. Pneum. suppl. i. p. 44), however, there appear 

 to exist sufficient differences to justify the separation of the two 

 forms specifically. C. cumllatus is considerably smaller, white, 

 the last whorl subangulate, the columella!" margin not diiatate, the 

 outer peristome is only called " reflexiusculum," whilst in my 

 species it is strongly recurved, &e. Otherwise the formation of 



