21 



This shell is generally found embedded in madre- 

 pore; the animal, though unknown, La Marck con- 

 jectures must occupy, in the first instance, the spiral 

 whorls, from which it altogether removes as necessity 

 requires an extension of the length of the tube, filling 

 up, at each stage of increase, the cavity previously 

 quitted, with solid testaceous matter, but not forming 

 partitioned cells or chambers, as some of the Serpu- 

 lae do; it occupies ouly the small portion of its last 

 addition. 



From these observations of La Marck it may rea- 

 sonably be presumed that the shell, in the first place, 

 is only buried to a depth sufficient to conceal the 

 whorls of the spire, at which time the terminal tube 

 would reach the surface of the madrepore in which it 

 is found (usually the Madrepora sinuosa); but in con- 

 sequence of the growth of tViat substance in a spheri- 

 cal form, the animal of the Magilus, in order to keep 

 pace with it, from the necessity of having a communis 

 cation open to the exterior surface of its retreat, is for- 

 ced to abandon the first plan of continuing the whorls 

 in a spiral direction, id which it never could have 

 reached the exterior; and, by prolonging the last one, 

 seeks an exit at the nearest opening. The lamellar 



