368 LITTOKINID.E. 



duced into large, long, arcuated, pointed auricles ; posteally it 

 becomes divided into two long, distinct tails or streamers, 

 nearly coextensive with the shell in its axial admeasurement ; 

 close to the bifurcation is a small opercular lobe without a 

 caudal cirrhus, on which is fixed a beautiful white horny sub- 

 oval operculum of 4-5 spires ; the first two or three are small 

 and concentrated, the last suddenly enlarges and closes the 

 aperture, and is marked with delicate oblique striae of growth. 

 The neck, when greatly protruded, is blotched at the sides 

 and on the top with a claret-coloured red : these marks, and 

 the eyes also, when not exserted, are conspicuous through the 

 tenuity of the shell. 



This rare animal, of which I have taken seven live examples, 

 dwells in a muddy-bottomed shelly district of the coralline 

 zone in Exmouth Bay, eight miles from shore, in 15 fathoms 

 water. 



This species has occasioned much difference of opinion; some 

 naturalists have thought it distinct ; others have considered it 

 the Montaguan R. vitrea in a perfect condition, and looked on 

 his shell as a specimen denuded of its striae by attrition. They 

 say that many of the so-called R. vitrea of the cabinets, when 

 placed under the microscope, exhibit traces of the striae of 

 the ' proximo, ' : in this fact they are probably correct, because 

 these smooth examples may really be that species ; but they 

 are wrong in their conclusions that it is Montagu's shell, as 

 will appear by the discovery of a perfect specimen and lively 

 animal of a species, which, I think, whatever doubts may still 

 exist, must now be considered the "smooth shell" of that 

 author, long known as the Turbo vitreus, and which has not 

 the slightest traces of spiral striae. The present difficulty has 

 arisen from Montagu's description suiting a worn 'proximo,,' 

 or the shell I propose to regard as the ' vitrea.' If I had 

 not made the present capture, I should, like others, have 

 judged the two to be different conditions of the same species ; 

 but I think it will appear, from what will be subsequently 

 stated, that even the shells of the ' proximo' and 'vitrea' 

 exhibit a slight but constant variation, and that the animals 

 are very distinct. 



