352 THE OCEAN WORLD. 



according to Mr. Bertram, is found in a variety of the mussel, which 

 is characterised by the valves being united by a broad hinge, and 

 having a strong fibrous byssus, with which it attaches itself to other 

 shells, to rocks, and other solid substances. "The pearl fisheries of 

 Scotland," he adds, "may become a source of wealth to the people 

 living on the large rivers, if prudently conducted." Mr. linger, a 

 dealer in gems in Edinburgh, having discerned the capabilities of the 

 Scotch pearl as a gem of value, has established a scale of prices which 

 he gives for them, according to their size and quality ; and it is now 

 a fact that the beautiful pearls of our Scottish streams are admired 



F'}g. 152. Pectunculus aureflua Fig. 153. Pectunculus Delessertii 



(Reeve). (Reeve). 



beyond the Orient pearl. Empresses and queens, and royal and noble 

 ladies, have made large purchases of these gems; and Mr. Unger 

 estimates the sum paid to pearl-finders in the summer of 1864 at 

 ;i 0,000. The localities successfully fished have been the classic 

 Doon, the Forth, the Tay, the Don, the Spey, the Isla, and most of 

 the Highland rivers of note. Scottish pearls are much whiter in 

 colour than Oriental. What tint they have is bluish, while those of 

 the East are yellowish. Pink pearls are produced by several exotic 

 species of Unio. 



The seventeenth family is that of the Trigoniadae, with the genus 

 Trigonia, of which so many species occurred in the Jurassic period 

 in the strata of Europe, but of which two or f .hree alone are now 

 left alive in the seas of Australia. 



The eighteenth family, the Arcadae, affords between 200 and 300 

 species of the genera of Leda, Nucula, Pectunculus, and Area. Of 

 these we shall only at present instance Pectunculus. 



