189i.j baker shells from the mauritius. 37 



Revision of the genus Magilus of Montfort. 



The genus Magilus has been somewhat of a puzzle, in many 

 respects, to Conchologists, and from its varying habits and the paucity 

 of material at the disposition of the student many errors in descrip- 

 tion have arisen. In the collection of shells dwelt upon in the first 

 part of this paper, was a suite of over a hundred Magili in all stages 

 of development from the very young shell, so thin and fragile that it 

 seemed as though a breath would break it, to the adult animal with a 

 heavy tube over a foot in length. From this collection and from a 

 number of specimens in my own collection, I have drawn up the fol- 

 lowing notes : 



Messrs. H. and A. Adams, in their " Genera of Recent Mollusca," 

 following Riippell, distinguished the genus Leptoconchus from Magi- 

 lus, the differential characters being that Magilus formed a tube and 

 possessed an operculum while Leptoconchus did not ; many of the full 

 grown specimens of Magilus antiqmts before me are strongly suggest- 

 ive of some of the species included by these authors in Leptoconchus. 

 However, should this character of the absence of operculum prove 

 constant, after the examination of a large quantity of fresh material, 

 the two genera should by all means be separated. 



Dr. Paul Fischer, in his Manuel de Conchyliologie, p. 648, separates 

 the two genera on account of the absence of the operculum in Lepto- 

 conchus, but acknowledges the difficulty of affixing the generic value. 



The animal of Leptoconchus is described as having a greatly 

 thickened and fleshy mantle margin ; tentacles small, broad and united 

 at their bases ; eyes small and black, on the outer side of the tentacles, 

 near their tips ; foot small, short, obtuse and rounded behind, with a 

 thin, expanded disc-like lobe in front ; the siphon is obsolete. Of four 

 individuals examined by Riippell two were males and two fen^^les. 

 The males were characterized by the presence of a straight, acumi- 

 nate verge, swollen and club-shaped at the extremity, placed on the 

 right side of the body. The presence of such an organ in a fixed 

 animal is very extraordinary and requires further investigation. 



Troschel was unable to discover any indication of armature upon 

 the lingual ribbon ; but this fact might be accounted for by their 

 sedentary habits, which would do away with the need of such an 

 organ, as their food must necessarily be brought to them by the cur- 

 rents ; and as they are attached, their food must be of a small, almost 

 microscopic character, as active animals could easily escape them, 

 and so the radula would gradually become reduced to a rudiment 



