282 HELICID^. 



country, possess ten or more full volutions, if it retained 

 all of them from the apex downward. But as fast as 

 the growth of the animal compels it to increase the num- 

 ber and volume of the whorls, it releases its connection 

 with the superior whorls, creates a new attachment lower 

 down, forms a new apex or spiral calcareous septum, which 

 separates it from the abandoned part ; and, in some man- 

 ner which is not understood, breaks and throws off those 

 whorls which are no longer of use. This commences at 

 a very early period ; the original apex being thrown off 

 when the shell has acquired five or six whorls. They 

 differ, in this particular, from the land shells, and espe- 

 cially from the Helices, which always, so far as I know, 

 retain their original attachment to the apex of the shell. 



It has been thought that the breaking of the spire, 

 after being left by the animal, and becoming dry and 

 brittle, is accidental ; but I conceive that the effect is 

 much too constant to be accounted for in that way. I 

 have never been able to find a mature specimen with the 

 apex. And in all the various countries which it inhabits, 

 including the whole southern part of Europe, the northern 

 part of Africa, the islands of the Mediterranean, the Cana- 

 ries, Madeira, &c., the same peculiarity attends it. If 

 it were only an accident, some few in this wide extent 

 might escape. I doubt not, therefore, that it is effected 

 by the action of the animal itself. It may be that the 

 calcareous matter of the shell is absorbed at the point 

 of division, previous to the formation of the new septum. 



Mr. Say made out his description from an immature 

 specimen. 



