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THE AUSTRALIAN MUSEUM MAGAZINE. 



has a series of ridges arranged in rings 

 around the shell. This whelk prefers 

 places where it can get the full force 

 of the sea's battering. 



The mouth of the shell of a whelk 

 is broken at the end furthest from the 

 apex of the shell by a deep notch, 

 through which an organ called the sip- 



Some of the periwinkles have almost 

 deserted the sea as a home, and especial- 

 ly is this the case with a very small 

 bluish-grey periwinkle {Meier aphe maii- 

 ritiana), which is found in clusters in 

 hollows well up on the rocks. It is only 

 covered by the highest tides and some- 

 times .only by the spray of them. It is 

 well on the way to becoming a land ani- 

 mal ; the land snail is a periwinkle 

 which has completed the change. 



The general internal structure of the 

 whelks and periwinkles is much the 

 same, the internal organs being gathered 

 together in a twisted hump which is 

 covered by the shell. The tongue is a 

 long ribbon working to and fro behind 

 the mouth opening. It is covered like 

 a file with rows of teeth — an enormous 

 number of them; some species of sea 

 snails have over 500,000 teeth. The foot 

 on which the animal glides is just a 

 flat creeping disc, and the creatures 

 move by a series of wave-like undula- 

 tions which flow along it. 



Limpets (Cellana variegata). 



To be found high and dry on the rock flats 



when the tide is out. 



Photo. — A. Musgrave. 



hon acts. This is a spout-like projec- 

 tion which enables the animal to re- 

 ceive the aerated water for breathing. 



The opening of the shell can be en- 

 tirely closed by a tightly fitting door 

 called the operculum, which the creature 

 draws into it. This operculum is a 

 characteristic feature of those Gastro- 

 poda (snail-like shell-fish with only one 

 shell). In the ease of the land snail, 

 the opening is closed in winter by a 

 hard layer of mucous matter called the 

 epiphragm. 



PERIWINKLES. 



Periwinkles may always be found 

 crawling about in the rock pools. In 

 the periwinkles, or sea snails, there is 

 no notch in the margin of the shell such 

 as is possessed by the whelks. The pre- 

 sence or absence of this notch is a fairly 

 sure guide to the feeding habits of these 

 creatures, for if the notch be present the 

 animal is almost certain to be carnivor- 

 ous, while, if it is absent, the animal is 

 a vegetarian. 



Chitons (Sypharochiton pellis-serpentis). 



In company with limpets and tubes of 

 Galeolaria occur these quaint "mailed" mot- 

 luscs. They are everywhere to be found 

 clustering together in small depressions on 

 the rocks, from about the mid to the upper 

 tidal zones. 



Photo. — A. Musgrave. 



