250 Major M. Connolly on 



these forms I hope to do something towards unravelling the 

 tangle that has existed with regard to them, and has made 

 the arrangement of StenogyrinEe one of the most difficult 

 branches of South-African conchology. 



A difficulty presenting itself at the outset is that of 

 deciding how much latitude can be allowed for local and 

 individual variation. As Dr. Pilsbry points out, some 

 members of the family are peculiarly subject to dimorphism, 

 two forms of the same shell, a slender and a stouter, with 

 intermediate degrees, all other features remaining the same, 

 often coexisting in the same locality. It is therefore ob- 

 viously impossible to attach much importance to mere differ- 

 ence in the breadth of two shells, although it may entirely 

 alter their general relative appearance. It must also be borne 

 in mind that the live shell of nearly every South-African 

 Stenogyroid in good condition is normally very pale bluish 

 green (olivaceous) in colour, very thin, nearly transparent, 

 with a bright gloss that varies from a high polish in the 

 smoother species to a duller silky sheen when the sculpture is 

 sufficiently pronounced to ridge, ever so slightly, the smooth- 

 ness of the shell. Even live specimens, if exposed to climatic 

 influence, are apt to lose their gloss and transparency and 

 take on a general yellowish tinge, often before maturity, 

 while dead shells soon become white and opaque, losing- 

 whatever gloss they originally possessed. Good live speci- 

 mens, too, are often so affected by immersion in spirit as to 

 lose much of their translucency, and become blotched with 

 creamy stripes or stains. 



Differences of the above nature, then, can only be regarded 

 as of a certain minor relative importance ; and the question 

 remains, how much notice must be taken, in the division of 

 the species, of the nature of their epidermis and sculpture, 

 breadth of apex, shape and number of whorls, amount of 

 perforation, and size and shape of aperture. With the excep- 

 tion of the last-mentioned, these points will be found to 

 remain almost constant in even a large colony of most species 

 under discussion, and to vary comparatively little in shells, 

 attributable to the same species, gathered from widely different 

 parts of the country ; it is therefore from a close study of 

 these details in particular that my inferences have been 

 drawn. 



In following the classification adopted by Dr. H. A. Pilsbry 

 in his ' Manual of Conchology,' vol. xviii., I may point out 

 that that author admits that the reference of certain species 

 to one or other genus has been in many instances purely 

 arbitrary. Some forms undoubtedly appear to be wrongly 



