78 MR. J. COSMO MELVILL ON 



but in Sowerby^s ^ Thesaurus^ (1870) 36 are mentioned. 

 Tryon^ of Philadelphia, in his elaborate monograph just 

 alluded to — the ' Manual of Conchology/ vol. vi. — calls but 

 17 of these true species, with 10 subspecies, and also cites 

 12 slight varieties, classed almost as synonyms, the total 

 number of named forms coming up to 39. Of these 37 

 are exhibited in the present collection. 



The subgenus Cylinder may be briefly thus charac- 

 terized : — 



Shell subconic, smooth, or very lightly striated ; spire 

 elevated ; whorls never coronated, numerous ; body-whorl 

 ventricose, notched at the suture ; aperture effuse at the 

 fore part. 



" The species,^^ writes Mr. Arthur Adams, " of this 

 section are all very rich in the style of their colouring, 

 and a somewhat similar reticulated kind of pattern runs 

 through the entire series." 



Some very widely differing Cones, e. g. C. arcMthalassus, 

 ammiralis, acuminatus, and cordigerus (a var. of nobilis) 

 among the Leptoconi, and G. arachnoideus and C nicoba- 

 ricus, among the Marmorei have a similar reticulated 

 pattern. All these differ, however, materially in form, 

 either, as in the last section mentioned, by the coronation 

 of the whorls, or, in the former, by the grooved and 

 sculptured spire, and more truly conical shape. 



The only species which presents any difficulty at first 

 sight is a variety of C. cordigerus (Sowb.), which, in the 

 specimen exhibited, approaches so nearly to C. omaria, 

 as to suggest a mimetic principle among the molluscs 

 similar to that which is known to exist in other branches 

 of the Animal Kingdom. 



The geographical distribution of Cylinder, so far as 

 known, is almost exclusively eastern, many species being 

 found ubiquitously in the eastern tropics, from E. Africa 



