252 TEOCEEDINGS OF THE MAL\COLOGICAL SOCIETY. 



tlie suture. The aperture is uniformly bluisli-whitc within. Length 

 (3 wliorls) 33, dium. 18 mm. 



Ilab. — Eandjermasin, South Borneo. 



Yar. fasciata. — Erot, loc. cit. p. 159; Bock, loc. cit. p. 635. Ahout 

 the same size or a little smaller than the type, dark brown, Avith three 

 broad bands, only slightly visible exteriorly, but distinct within the 

 aperture : these do not quite I'each the margin of the lip, which is 

 white. The surface of the shell is smooth, with the exception of one 

 or two strife below the suture. 



Hab. — Same as preceding variety. 



Yar. funesta. — H. Adams, Proc. Zool. Soc. 1861, p. 383, as a distinct 

 species. Rather smaller than type, with a less distinct infra-sutural 

 ridge, and a nearly smooth epidermis. Under a strong lens, the 

 epidermis of the type exhibits very fine, and minutely granular lines of 

 growth, but in the present variety scarcely a trace of such granulation 

 is visible. Length 19, width 11 mm. 



JIab. — Malacca (H. Ad.) ; Sarawak (C. Hose in Brit. Mus.). 



Var. parva. — Much smaller than type ; spire much eroded, with 

 only two or thi-ee whorls remaining ; transversely faintly striated 

 throughout, a few striae below the suture very distinct ; scarcely any 

 minute granulation. Length of specimens, consisting of two whorls 

 only, 14-17 mm. 



ITah. — N. Borneo, probably some part of Sarawak (A. Everett). 



Var. granulata. — Same size as var. parva, but having the surface 

 more strongly grooved throughout, the intervening ridges, crossed 

 by lines of growth, being more or less distinctly granular. Scarcely 

 a trace of minute granulation. 



Mab. — Busau, West SaraAvak (A, Everett). 



Var. JYatmiensis. — Smaller and narrower than type, averaging 

 about 20 mm. in length, less constricted below the suture, whilst the 

 minute granulation of the surface is perhaps a trifle finer and more 

 regularly spiral in its arrangement. 



Hab. — Sirhassen Island, Natuna Group (A. Everett). 



This is one of those cases in which the systematic zoologist is 

 puzzled to decide upon the proper course to pursue — whether to 

 create a number of so-called distinct species, or to regard the 

 various forms in the light of varieties. Dr. Brot, who has had great 

 experience with fresh-water mollusca, has refrained from describing 

 as tlistinct species two of the forms eniimerated, and consequently 

 I am inclined to follow his example, consideiing it more philosophic 

 to await further evidence, than is furnished by the shells, before 

 regarding the varieties in question as separate species. True, the 

 ditference between the var. maxima and the vars. parva or Katunensis 

 is enormous ; still, taking into consideration the well-known great 

 variation which obtains among fresh-water shells generally, and the 

 strong probability of the future discovery of other intermediate 

 connecting links, 1 think it advisable to consider these fonns in 

 the light of varii'ties of one and the same polymorphous species. 



Mr. Carl Bock (Proc. Zool. Soc. 1881, p. 635) noticed with regard 

 to tlie varieties Avhich he collected, tliat only in young shells the 



