SHELLS AND MOLLUSCOUS ANIMALS. 195 



Heeren, " the passion for the elegant luxury was 

 at its height about the period of the extinction of 

 Roman freedom, and they were valued in Rome 

 and Alexandria as highly as precious stones. In 

 Asia this taste was of more ancient date, and may 

 be traced to a period anterior to the Persian 

 dynasty. A string of pearls, of the largest size, 

 is an indispensable part of the decorations of an 

 Eastern monarch. It was thus that Tippoo was 

 adorned when he fell before the gates of his capital; 

 and it is thus that the present ruler of the Persians 

 is usually decorated." Pearls have one disadvan- 

 tage, however, that they lose their lustre in the 

 course of years, especially if worn near the skin. 

 The pearls found in our native species of oysters 

 are far inferior to those brought from the Persian 

 Gulf, from Ceylon, or any of the Oriental pearl 

 fisheries, and have, generally, a milky and more 

 opaque appearance. 



We have several British species of oyster, and 

 the shells of some of those of distant countries are 

 highly prized by conch ologists. A shell termed 

 the hammer-oyster (Malleus vulgaris), from the 

 Indian seas, is not uncommon in collections, and 

 in some specimens the shell is shaped so much like 

 a hammer as to lead to its immediate recognition. 



Several species of the scallop are abundant in our 

 seas, and their shells are strewed about on our 

 shores. Cuvier called these shells the butterflies 

 of the ocean, not so much because, when the two 

 valves are expanded, they in some respects resemble 

 the wings of our summer-insect, as that they ex- 

 hibit such various and beautiful colours. Numbers 

 of the little shells belonging to the speckled scallop 

 (Pecten varia), are to be found on almost any part 

 o2 



