r 



106 THE FAMILY AQUAKIUM. 



well as composed the draught he finally directed for him- 

 self, but had not the courage to swallow. 



The Trochus tribe, vulgarly known as Tops, are as use- 

 ful as the Periwijikles. They have evenly-conical shells, 

 from the peculiar shape of which they derive their names. 

 The T. cinerarius is of a dull purplish grey, marked with 

 zig-zag lines. The T. umbilicatus is of a dull olive or 

 green, with narrow, reddish bands radiating from the 

 centre. The shells have a remarkably pearly appearance 

 inside, while not a few are strikingly finished off with 

 iridescent tints, and brilliant changeable shades of the 

 nacreous character. The T. ziziphinus, or Pearly Top, 

 is of a rich orange color, striped with black. The most 

 profitable to the Aquarium is the T. cinerarius^ who, if 

 you have a good pocket-lens, will be found a busy 

 little customer. The Tops and the Periwinkles, when 

 viewed through a proper instrument, may be seen putting 

 forth their probosces and turning them inside out, like a 

 stocking, until the silky surface, which is the tongue, en- 

 counters the glass sides of the tank. Here each proboscis 

 makes a grand sweep, like a mower with his scythe, tak- 

 ing up in its swath all the mass of confervse on the 

 spot. When the proboscis infolds its walls the tongue 

 disappears, and with it goes to the interior all the col- 

 lected material. A forward movement is made, and 

 another portion of the glass swept clean, after a similarly 

 unique fashion, until, having reached the end of their field 

 of industry, they recommence again. 



