THE STAIRCASE WENTLETKAP 



391 



mode in which the molluscs build up their wonderful homes. It looks, indeed, much as 

 if it were in the preliminary stage of shell-making, and had completed its arrangements 

 with the exception of pressing the whorls together. When young, the spiral form is 

 tolerably regular, but as it grows in years its regularity decreases, and the shell exhibits 

 the form represented in the figure which occupies the centre of the engraving. 



The aperture of the Worm-shell is round, and the operculum is consequently circular, 

 and fits the opening with tolerable closeness. Its external face is concave. When not 

 open, the tube is found to be supplied with many partitions of the same material as its 

 walls. The colour of the Worm-shell is greyish yellow. 



TURRITELLA. Turritella communis. SNAKE-SHELL. Siliqudria anguvna. 



WORM-SHELL. Ve.rm.iius lumbricdlis. 



ON the extreme right of the engraving may be seen a shell of somewhat similar 

 construction, but readily distinguishable by the longitudinal slit which extends throughout 

 its entire length. About seven species of the Siliquaria are known, all of which are 

 carnivorous in their habits, and are found within sponges. As in the last species, the 

 SNAKE-SHELL is regularly spiral at its commencement, where it was constructed by the 

 animal in its youth, but loses its regularity in exact proportion to its age. Its colour is 

 whitish. The small head is shown just protruding, and exhibiting the stopper-shaped 

 operculum. 



THE lower figure in the engraving on page 392 represents the empty shell of the 

 STAIECASE or PKECIOTJS WENTLETKAP, in former days one of the scarcest and most 

 costly of the specimens of which a conchologist's cabinet could boast. There was hardly 

 any sum which a wealthy connoisseur or virtuoso, as the fashion was then to call those 

 who were fond of natural history, would not give for an especially large and perfect 

 example of this really pretty shell Now, however, its glory has departed, for a tolerably 

 good specimen may be procured for a few shillings, and a Wentletrap which would a few 

 years ago have been sold for fifty pounds can now be purchased for fifteen shillings. 



Putting aside, however, the question of rarity or cost, this shell is a very interesting 

 one, both for its beauty and the mode of its construction. Tt is purely white and partly 

 transparent, the elevated ridges being of a more snowy white than the body of the shell, 



