342 THE OCEAN WORLD. 



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

 he acids, " 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 beyond the 

 orient pearl. Empresses and queens, and royal and noble ladies, have 

 made large purchases of these gems ; and Mr. linger estimates the 

 sum paid to pearl-finders in the summer of 1864 at 10,000. 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. 



Our seventeenth family are the Trigoniadae, affording Trigonia, of 

 which so many occurred in the Jurassic period of Geologic History in 

 the strata of Europe, but of which two or three are alone left alive in 

 the seas of Australia. 



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

 species of the families of Leda, Nucula, Pectunculus, and Area. 



Of the eighteenth family, Arcadae, we shall only at present instance 

 Pectunculus. 



The genus Pectunculus are abundant on the shores of the Mediter- 



Fig. 153. Pectunculus aureflua Fig. 154. Pectunculus delessertii 



(Reeve). (Reeve). 



ranean and along the Atlantic coast. If we take up at hazard a 

 handful of shells on any part of the French coast, one-third will consist 



