392 



THE COMMON PEKI WINKLE 



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. 



THE smaller figure, showing 

 the shell attached to the animal, 

 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 eleva- 

 tions, which, however, are not 

 nearly so bold as those of the 

 preceding species, but thick in 

 proportion to their height, set ob- 

 liquely 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 ten- 

 tacles. The foot is triangular, 

 with the front rather obtuse, and 

 supplied with a fold. When dis- 

 turbed 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 colour 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 Litorinidse, or Shore Molluscs, because 

 the greater number of them frequent the coasts, and feed upon the various algse. The shell is 

 always spiral and never pearly, by which latter characteristic it may be distinguished from 

 certain shells belonging to another family, but somewhat similar in external appearance. The 

 aperture is rounded. The animal has its eyes set at the outer bases of the tentacles, and 

 the foct 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 PEKIWINKLE (Litorina h'torea) 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 



STAIRCASE WENTLETRAP. -Scalaria pretiona. 

 COMMON WENTLETRAP. Scalaria communis. 



