MACJIIAJS. 215 



cles are small, broad and united at their bases ; the eyes ai-e small 

 and black, on the outer side of the tentacles, near their tips ; the 

 foot is small, short, obtuse and rounded behind, with a thin, 

 expanded, disk-like lobe in front, and the siphon is obsolete. 

 The genus ditfers from Gampvlotus {Ma(jilus) not ovXy in the 

 alisence of the operculum, but in the shell never forming a long 

 tubular projection of the mouth as in that genus. It comprises 

 but few species, which take up their abode in corals and madre- 

 pores. 



Desha3^es, in his " Concholog}' of the Island of Bourbon,'' 1862, 

 describes a number of species of Leptoconchus as well as the 

 anatomy of one of them, confirms the non-existence of the oper- 

 culum and sustains the separation from Magihis. 



On the other hand, that expei'ienced conchologist, Mr. G. B. 

 Sowerby, in his introductory remarks upon the genus Magilus, 

 in Conch. Iconica, xviii, 1872, unites Leptoconchus with that 

 genus. He says : 



The habits of this genus of mollusca are very curious. The 

 young fry, after a short period of free locomotion, seems to find 

 its way into some hole in a growing madrepore, and then to 

 become stationary ; but as the substance grows around it, it 

 would soon become enclosed imless the growth of the shell kept 

 pace with that of the madrepore. In order, therefore, to keep 

 its aperture close to the surface, the two lips are extended in the 

 same direction in the form of an irregular tube. The Magilus 

 leaves its shell in the original cavity, and filling it up (with shelly 

 material) 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 con- 

 solidated 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 

 separated 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 



