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 
different. 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. 
MaaiLina, Vélain. 
Distr.—M. serpuliformis, V lain (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 the animal may prove to have no rela- 
