120 MURICID^. 



shell in the original cavity, and filling it up (with shelly mate- 

 rial) so that it becomes solid, occupies only that portion of the 

 tube which is nearest to the opening. The walls of the tube are 

 thickened, and the portion which represents the canal is consol- 

 idated into a thick keel. The species which have not been found 

 as yet in an advanced state, and which appear generically to 

 resemble the young shells of Magilus antiquus, have been sepa- 

 rated by authors under the generic term Leptoconchus ; and it 

 is asserted that while the Magilus possesses an operculum, the 

 Leptoconchi do not. It is also said that the young shell of the 

 Magilus begins to form a thickened and entire edge to its aper- 

 ture, as if preparing for the future erratic course of its shell. It 

 appears to me, however, that it depends upon the accidental 

 conditions of habitat and growth whether and at what period of 

 life the shell of a Magilus shall become tubular ; and as for the 

 operculum, it is certain that some, if not all, the species enumer- 

 ated as Leptoconchus by authors have been found with opercula ; 

 notably, L. Lamarckii, Desh. The Isle of Bourbon, the Mauri- 

 tius and Sandwich Islands — perhaps most islands with reefs — 

 afford homes to the Magili." 



We agree with Mr. Sowerby ; indeed, it would be impossible 

 to designate from the shells which species should be referred to 

 Leptoconchus and which ones to the juvenile condition of 

 Magilus. It is probable that the development of the tube is 

 accidental, and it is equally probable that, as in Conus, the oper- 

 culum is not always developed. Troschel has not discovered 

 any indication of armature upon the lingual ribbon. So irreg- 

 ular are the shells of the Magili, and so much is their growth 

 influenced by the circumstances of their habitation, that all the 

 species that have been differentiated from M. antiquus must be 

 regarded with suspicion. When numbers of specimens, from 

 difi'erent localities, and collected with a view to coalescence 

 rather than to differentiation, shall have been compared, we shall 

 be able to assign definite places to the species which we are now 

 compelled to take on probation. 



Magilina, Velain. 

 Distr. — M. serpuliformis, Velain (xliv, 37, 38 '. Indian Ocean, 

 Young shell free, formed of a single whorl ; finally prolonged 

 into a tube which is attached by one side to the surface of sub- 

 marine bodies. 



The species which forms the type of this genus is much smaller 

 than those of Magilus. The distinctive characters consist in the 

 spiral shell having one whorl only and in the fixed adult being- 

 attached by one side of the tube to the external surface of sub- 

 marine objects, instead of growing in their interior. This is a 

 great change of habit, and tlie animal may prove to have no rela- 



