392 



on account of their superior thickness, which does not permit the light to pass through 

 them as in the case of the thinner body. The whorls of this shell are separate from 

 each other, and apparently bound together only by the projecting ridges, so that the 

 general appearance is as if the whorls of a worm-shell had been pressed nearly together, 

 and then kept in their place by a succession of shelly elevations. This beautiful shell 

 is found in the Indian and Chinese seas. 



STAIRCASE WENTLETRAP.-Scafarla pretlosa. 

 COMMON WENTLETRAP.-Sca/ar/a com munis. 



THE smaller figure, showing 

 the shell attached to the ani- 

 mal, represents the COMMON 

 or FALSE WENTLETRAP, a 

 species tolerably common 

 upon our coasts. 



In this shell the whorls are 

 united together and furnished 

 with a number of circular 

 elevations, which, however, are 

 not nearly so bold as those of 

 the preceding species, but 

 thick in proportion to their 

 height, set obliquely on the 

 shell, and smooth. 



The animal has a proboscis- 

 like mouth, which can be re- 

 tracted at the will of the owner ; 

 the tentacles are tolerably 

 long, placed near together ; 

 and the eyes are set near the 

 base of the tentacles. The 

 foot is triangular, with the front rather obtuse, and supplied with a fold. When 

 disturbed or alarmed, the creature is capable of exuding a dark purple fluid. Nearly 

 one hundred species of Wentletrap are known, all the largest examples being found in 

 tropical regions. They live at a considerable depth, sometimes being captured 

 in eighty fathoms of water, and little seems to be known of their habits. 



The color of the Common Wentletrap is rather varied. Sometimes it is dull white, 

 sometimes it is very pale brown, and in a few specimens the shell is reddish violet, with 

 the ribs purple. 



WE now arrive at another family, termed the Litorinidae, or Shore Molluscs, because 

 the greater number of them frequent the coasts, and feed upon the various algae. The 

 shell is always spiral and never pearly, by which latter characteristic it may be distin- 

 guished from certain shells belonging to another family, but somewhat similar in ex- 

 ternal appearance. The aperture is rounded. The animal has its eyes set at the 

 outer bases of the tentacles, and the foot is remarkable for a longitudinal groove along 

 the sole, so that in the act of walking each side advances in its turn. The tongue is 

 rather long, and is armed with a formidable series of sharp teeth that serve admirably 

 for the purpose of scraping away the vegetable matter on which the animal feeds. The 

 operculum is horny, and rather spiral. 



THE common PERIWINKLE (Litorina litbrea) is the most familiar example of this family, 

 and is too well known to need any detailed description. The Periwinkle is found upon 

 our rocks in great profusion, occupying the zone between high and low water, and always 

 being found near the edge of the tide. There is, however, another species (Litorina rudis} 

 which occupies a rather higher zone than the previous species, and which, though very 

 plentiful, is not eaten, in consequence of its young obtaining their shells before eggs are 

 laid, and having a gritty and unpleasant effect upon the teeth. Sea birds, however, are 



