ASHFORD : ON BANDED LAND SHELLS. 93 



any attempt to display a species in natural sequence in a 

 museum the var. bizona should stand at the head of the series 

 representing B. acutus. The same applies to the clear banded 

 var. oi H. caperata. they were once typical but simply from decrease 

 of numbers have become varietal. In the cases of B. virgata. 

 and ertcetorum the changes of surface have made slower progress 

 and those individuals which retain the zones unbroken, still form 

 the majority of their kind. An examination of the var. bizona of 

 B. acutus however reveals the fact that their bands are more or 

 less giving way. The colony of them on High Down near, 

 Freshwater, though numerous, occupy but a limited nook; and 

 though among themselves they doubtless produce bizonas "after 

 their kind," yet from constant intercourse with their less richly 

 ornamented neighbours, which surround them and to some extent 

 wander into their pasture ground, it is not difficult to foresee a 

 time when their posterity will have become undistinguishable from 

 the prevailing type, while ages will probably pass before the band- 

 ed individuals of H. ericetorum become a mere variety of their 

 kind. 



A not unnatural arrangement of the variations of these species 

 would therefore seem to be after this manner : — • 



Specimens with cojitimwus upper band: 



I 2 



A — Band just breaking into beads. 



i 

 B — Band fairly broken into beads. 



1 

 C — Band eliminated on upper whorls. 



CC — Band just perceptible. 



I 

 D — Without upper band. 



E — Band breaking into segments. 



I 

 F — With severed portions more 



I [diffused. 



G — Still more diffused.* 



I 

 GG — Whole surface marbled. 



I 

 H — Monochrome shell. 



*Many shells, having reached this stage of diffusion, appear to degenerate, 

 the patches becoming gradually obliterated till section D is reached though 

 a different channel. 



