78 



posed of five or six very little raised volutions, 

 terminating abruptly, as if many of the lower ones 

 had been broken off by violence ; the extremity 

 closed : aperture oblong-oval, with hardly any 

 umbilicus. 



Young shells have a very obtuse summit, and appear 

 to shed or exfoliate their ultimate volutions as 

 they advance in age. 



The earlier conchologists were not well agreed as to 

 the cause of this singular truncation of the ex- 

 tremity. Linne considered it as a law of nature, 

 because the upper extremity was always found 

 closed up. Muller, on the contrary, declares he 

 has full conviction. that it is the effect of accident, 

 and that it had previously existed in a perfect 

 state. Murray agrees with Linne, observing that 

 whenever a portion is broken from a spiral shell, 

 that part is always left open. If this were the 

 mere effect of accident, it would appear singular 

 that all, at the same period of growth, should 

 meet with the same accident, in the same portion 

 of the shell. The probability is, that as the animal 

 enlarges in its growth, it gradually recedes from 

 the smaller volutions, closing them up, joint after 

 joint, in its retreat, leaving these neglected portions 

 without vascular connexion, and subject to exfolia- 

 tion like the leaves of a deciduous tree, or like the 

 shedding of teeth. 



