Reference List of South African Non-marine Mollusca. 65 



very slight peculiarities of form, sculpture, or dentition. However, 

 in the recently described E. Johannesburg ensis, M. and P., it will be 

 found that, while the form and sculpture change but little, the 

 presence or complete absence of the basal tooth, even among shells 

 from under the same stone, is a matter of indifference ; while in 

 E. xysila, M. and P., though the dentition remains practically 

 unchanged, the length of full-grown specimens varies from 5 to 

 8 mm., and the sculpture is sometimes almost lirate, sometimes 

 almost invisible, quite irrespective of the size of the shell. 



It can be easily understood, therefore, that, in more widely distri- 

 buted species, the range of variation increases with the extended 

 geographical distribution ; but in many such cases intermediate 

 varieties are found in intermediate localities, which link up a 

 complete chain of connection between comparative extremes 

 of form. 



Taking these facts into consideration, it is highly probable that 

 many species at present reckoned distinct will, on fuller comparison, 

 have to be referred to merely varietal rank. 



As no satisfactory method of subdividing the South African 

 Enneinae has yet been contrived, the subjoined list of species 

 is given in alphabetical order, omitting all reference to any sub- 

 genera or sections hitherto proposed. 



7. ENNEA ADAMSIANA, Pfeiffer. [S.A.M.] 



1859 Ennea adamsiana, Pfr., Novit. Conch, i. p. 114. pi. 32, f. 9-11. D.F. 



1859 Mon. Hel. iv. p. 339. I). 



1885 Tryon, Man. of Conch, i. p. 98. pi. 19, 



f. 85. D.F. 

 1904 ,, Kob., Couch. Cab. p. 192.pl.24,f.8. D.F. 



Type in British Museum. 



Hab. NATAL. Port Natal (in coll. Pfeiffer). Widely distributed. 



CAPE OF GOOD HOPE. " Said to be found at Korsten, Tort Eliza- 

 beth " (Crawford). 



var. IMPEBVIA, Melv. & Pons. [S.A.M.] 



1896 Ennea impervia, M. &P., A.M.N.H. xviii. p. 315. pi. 16, f. 1. D.F. 

 1904 Kob.,Conch.Cab.p.233.pl.32,f.21. D.F. 



Type in British Museum. 



Hab. NATAL (fide M. & P.). Lower Urnkomaas; Equeefa ; Port 

 Shepstone (Burnup). 



APE OF GOOD HOPE. Port St. John's (Shortridge). 



