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MOLLUSCS. 



its prey whole, shell and all. The shell is then broken up by the aid of a very re- 

 markable gizzard, and the soft parts digested. This gizzard consists of three strong 

 calcareous plates of different size and form, which grind against one another by 



powerful muscles. The shells of Scaphander 

 are mostly thin, spirally striated, oblong, 

 convolute, without any visible spire, having 

 the aperture narrow behind, and much wider 

 in front. The known species are not 

 numerous, and occur chiefly in seas of the 

 Northern Hemisphere, but a few have been 

 described from other parts of the world. 

 S. mundus was obtained at the Aru Islands, 

 at a depth of eight hundred fathoms, and 

 & gracilis off the Azores, in one thousand fathoms. By far the largest known 

 form is the common British S. lignarius, which ranges from Finmark to the 

 Mediterranean. 



The bubble-shells (Bullidw), as this group is popularly called, are something 

 like Scaphander in form, but rather rounder and stronger in their structure. 

 Most of those belonging to the typical genus Bulla are prettily painted with 

 blotches, clouds, and dots. The animal is not too large for its shell, has distinct 

 eyes, and a different type of radula to that of Scaphander, which these molluscs 

 resemble in their predatory habits. Another genus is represented in Britain by 



larva OP Entoconcha (much magnified). 



Acera bullata (twice naft size). 



Acera bullata, which occurs on oozy ground and mud-flats in many estuaries. It 

 also ranges from Finmark to the Mediterranean; and is remarkable for its thin, horny, 

 convolute shell, with a slit at the suture, through which the animal protrudes a 

 long, thread-like mantle -appendage. The side -lobes are largely developed, and 

 can be reflexed so as to completely envelop the shell. They are also employed in 

 swimming. Another family is represented by Ringicula, all the members of 

 which are very small, not a quarter of an inch in length. The shells are entirely 

 white, more or less globular, with a pointed spire, and with the aperture* — which is 

 notched in front — to some extent contracted with folds. The channelled character 

 -of the aperture is rather exceptional, the shells of the Tectibranchs being almost 



