SMALL SHELLS. 217 



bigger than those now existing. Their resemblance to 

 Nautili and Ammonites is merely one of analogy. 



Drift-sand should also be closely examined for shells 

 of the more minute Gasteropodous Mollusca. A wonder- 

 ful variety of minute spiral univalve shells is found on 

 our shores ; though they are scarcely of so small a size 

 as to come within the list of genuine microscopic objects. 

 A simple pocket lens is sufficient to ascertain the charac- 

 ters of most. The different kinds of Rissoa, formerly 

 included in the multifarious genus Turbo, are elegant 

 little shells, whose spiral coils are variously sculptured 

 or ribbed, sometimes in a very elaborate manner. Mr. 

 Alder* has figured and described a considerable number 

 of these small shells, many of them collected from drift- 

 sand. Others may be obtained by the gatherers of sea- 

 weeds with little trouble, if they will only presei*ve the 

 sediment that collects in the water in which their sea- 

 weeds are washed. The Rissoce are vegetable -feeders, 

 and live among the branches of the smaller sea-weeds, 

 which are sometimes found as thickly covered with 

 them as bushes are with snails. When the sea- weeds 

 are plunged into fresh water, the Hissoce are quickly 

 killed and fall to the bottom, and may then be secured 

 by simply straining the water through a piece of canvas. 

 Many other minute and curious animals, and sometimes 

 Diatomacece, may be collected in a similar way. 



Among the animated wonders of the sea, though not 



all of microscopic size, few tribes are more singular in 



structure and in their history, or more beautiful in their 



varied forms, than the Acalephce, or Jelly-fishes, to whose 



* "Annals Nat. Hist.," 1st Series. 



