WENTLE-TRAPS, &c. 205 



WENTLE-TRAPS, &c. 



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

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

 temperate 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. 



PERIWINKLES. 



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. 



