184 The Museum Gazette 



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Others think that the sponge bores by grinding its spicules 

 against the softer limestone ; finally, it is supposed that the 

 power of contractibility of this sponge is no mean aid in the 

 work of excavation. Choanites, fossil sponges in chalk flints. 

 They frequently occur in the semi-transparent " brooch 

 pebbles" amidst the shingle at Brighton, Bognor and 

 Worthing. 



V. Shells. — In addition to the common shells of the sea- 

 shore, described and figured in our pages, our marine depart- 

 ment contains egg-cases or capsules of carnivorous mollusca. 

 These are tough and leathery, and of varied shapes, and each 

 contains many eggs. The best known are those of the whelk 

 (Buccinum imdatum), sometimes in bunches as large as one's 

 fist ; the dog- whelk (Purpura lapillns), the capsules of this 

 species " are like delicate pink grains of rice, set on tiny 

 stalks. They are not attached to one another, but are set 

 closely together in groups in sheltered nooks of the rocks. A 

 single Whelk has been observed to produce 245 capsules ! " 



Boring shells and examples of their work, including : (a) A 

 mass of hard rock extensively bored by the Piddock or 

 " Paper shell " (Pholas). The shells may be seen at the 

 bottom of some of the holes, and are projecting from others. 

 (b) A piece of wood bored by the "Ship-worm" (Teredo). 

 The burrow is lined with a thin shell of white paper. The 

 " Ship-worm " is not a worm, but a true mollusc, with a 

 bivalve shell, which, however, is so small that it was long 

 mistaken for its jaws. Its body is almost wholly outside the 

 shell. It does not bore stone, but only wood, and is very 

 destructive to piers, &c. 



Mussel shells with the byssus attached. The byssus con- 

 sists of silky threads used by the animal to anchor its shell. 

 The manner in which these threads are made may be readily 

 observed in an aquarium. The tongue secretes a fluid, which 

 is poured into a groove or canal, forming a deep longitudinal 

 furrow extending the length of the tongue ; in the canal it 

 dries into a solid thread. " The workmanship of land and 



