206 POPULAR CONCHOLOGY. 



an operculum.* 1 species, 

 recent. 



When in the young state 

 this curious shell presents 

 all the characters of a regu- 

 lar spiral univalve. The 

 animal establishes itself in 

 the excavations of madre- 

 pores ; and as the coral 

 increases around it, the 

 Magilus is obliged, in order 

 to have its aperture on a 

 level with the surrounding 

 surface, or near it, to con- 

 struct a tube, the growth 

 of the coral determining 

 its length. As this tube 

 goes on increasing, the animal abandons the 

 spiral for the tubular part of the shell ; and in the 

 operation it leaves behind no partitions, but 

 secretes a compact calcareous matter, which 

 reaches to the very summit of the spiral part ; 

 so that in an old specimen the posterior part of 



* Dr. Riippell. 



