WENTLE-TRAPS, &c. 205 



WENTLE-TEAPS, &c. 



The Tower-Shell and the Worm-Shell of the West 

 Indies, and the true Wentle-traps of the tropical and 

 i^emperate seas, belong in this group. The Royal 

 Staircase, or Wentle-trap, Figure 392, was formerly 

 very valuable. A specimen has been sold for a hun- 

 dred pounds sterling, although it is now worth only a 

 few dollars. 



PEEIWINiaES. 



Periwinkles live in the sea near the shore. Two 

 species are shown in Figures 394 and 395. They feed 

 on algae, — marine plants. 



RIVER SNAILS. 



These live in fresh waters, and have the shell cov- 

 ered with a green skin. They bring forth their young 

 alive, and the little embryo snails, even before they 

 are born, and when so small that they can scarcely be 

 seen without a microscope, have a perfectly formed 

 shell, a " foot " and operculum, delicate tentacles, and 

 distinct black eyes. 



VIOLET-SNAILS. 



The Violet-Snails live together in large numbers, in 

 the open sea, where they float by means of many air- 

 vessels, which form a raft, a, Figure 404. The shell 

 is thin, the base deep violet color, and the spire almost 

 white. They yield a violet dye. 



LIMPETS. 

 Limpets are found clinging tightly to stones and 

 other shells, and move about but little or not at all. 



