240 



Shell Life 



Auger-shell 

 (two-thirds nat. size) 



{Turritella) is the one to which Pennant gave the 

 name of the Auger {T. communis), on account of its 

 resemblance to that boring implement. It is a giant 

 compared with the little Horn- 

 shells. The whorls are spirally 

 ridged, the mouth comparatively 

 small and round, though with a 

 suggestion of squarishness, and 

 without a canal or groove. The 

 operculum is round and horny. 

 The mantle is fringed with a 

 triple row of fine filaments. As 

 the new whorls increase in size to 

 accommodate the growing animal 

 the older whorls at the top of the 

 spire, being too narrow for occupation, are partitioned 

 off by the deposit of shell internally. It occurs on 

 all our shores above sand and mud in from 3 to 100 

 fathoms. 



We have just mentioned how the owner of an old 

 house shuts off the rooms that are no longer large 

 enough for use, more spacious apartments having 

 been erected. Some other species having thus 

 partitioned off the old from the new, deliberately 

 knock the older portion against stones in order to 

 break it off; in other cases the making of 

 the dividing wall appears to cause the older 

 part to perish. Shells that have undergone 

 this process are said to be decollated. 

 Perhaps the case of the Blind-shell (Cwcum 

 trachea) is still more remarkable, as the entire 

 appearance of the shell is altered by the conduct 

 of the animal. It besfins life with a shell coiled 



Blind-shell 

 (enlarged) 



