CONCHIFERA. 261 



R. Panama, &c. Manilla is the chief port to which they are taken. There 

 are three principal kinds, which are worth from £2 to £4 per cwt. : 1. 

 the silver-lipped, from the Society Ids. of which about 20 tons are annually 

 imported to Liverpool ; 2. the black-lipped, from Manilla, of which 30 tons 

 were imported in 1S51 ; 3. a smaller sort from Panama, 200 tons of which 

 are annually imported; in 1851 a single vessel brought 840 tons. (T. C. 

 Archei'.) These shells afford the " mother- o'-pearl" used for ornamental 

 purposes; and the "oriental" pearls of commerce (p. 38). Mr. Hope's 

 pearl, said to be the largest known, measures 2 inches long, 4 round, and 

 weighs 1800 grains.* Pearl-oysters are found in about 12 fathom water ; 

 the fisheries of the Persian Gulf and Ceylon have been celebrated from the 

 time of Pliny. 



Malleus, Lam. M. vulgaris, PI. XVI. fig. 20. The " hammer-oyster" is 

 remarkable for its foi-m, which becomes extremely elongated with age ; both 

 ears are long, and the umbones central. "VYhen young it is like an ordinary 

 Avicula, with a deep byssal notch in the right valve. 6 sp. China, Australia. 



Vulsella, Lam. V. lingulata, PL XVI. fig. 21. Syn. Eeniella, Sw. 

 Shell oblong, striated, sub-equivalve ; umbones straight, earless. Often 

 found imbedded in living sponges. Bistr. 3 sp. Eed Sea, India, Australia, 

 Tasmania. Fossil, 4 sp. U. Chalk — . Brit. France. 



Pteroperna, Lycett, 1852. P. costatula, Desl. Shell with a long pos- 

 terior wing; hinge-line bordered by a groove; anterior teeth numerous, 

 minute; posterior 1 or 2, long, nearly parallel with the hinge-margin. 

 Fossil, 3 sp. Bath oolite ; Brit. France. 



? Aucella (PaUasii) Keyserling, 1846. {Monotis, Miinster, not Bronn.) 

 Very inequivalve ; left umbo prominent, earless ; right valve small and flat, 

 with a deep sinus beneath the small anterior ear. Fossil, Permian — Gault. 

 Europe. " In A. cijgnipes we find no trace of prismatic cellular structure or 

 nacre, but the coarsely corrugated and somewhat tubular structure of the 

 Pectens." {Carpenter) 



Amhonychia (bellistriata) Hall, 1847. Nearly equivalve, gibbose, oblique, 

 obtusely winged. A. vetusta (Inoceramus, Shy.) is concentrically fur- 

 rowed ; the right valve has a small anterior ear (usually concealed) separated 

 by a deep and narrow sinus. Fossil, 12 sp. L. Silurian — Carb. U. S. Europe. 



? Cardiola (interrupta) Broderip, 1844. Equivalve, gibbose, obliquely 

 oval, radiately ribbed ; beaks prominent ; hinge-area short and flat. Fossil, 

 17 sp. U. Silurian — Dev. U. S. Europe. 



? Eurydesma (cordata) Morris ; Devonian? N. S. Wales. Shell equivalve, 



* Sections of oriental pearls exhibit very fine concentric laminae surrounding a 

 grain of sand, or some such extraneous matter ; the nacreous lustre has been attri- 

 buted to the diflFraction of light from the out-cropping edges of the laminae, but Dr. 

 Carpenter has shown that it may result from the minute plication of a single lamina. 

 (See fig. 23, p. 38.) 



