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 1851 ; 3. a smaller sort from Panama, 200 tons of which 

 are annually imported; in 1851 a single vessel brought 340 tons. (T. C. 

 Archer.) 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 form, which becomes extremely elongated with age ; both 

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

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



Vulsella, Lam. V. lingulata, PI. XVI. fig. 21. Syn. Reniella, Sw. 

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

 found imbedded in living sponges. Distr. 3 sp. Red 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. 



?-3fowa?fo (Pallasii) J&gsss&Rg, 1846. (Monotis, Minister, not Bronn.) 

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

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

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

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

 Pectens." (Carpenter?) 



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

 obtusely winged. A. vetusta (Inoceramus, Sby.) 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. TJ. 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. TJ. 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- 

 bited to the diffraction 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. 

 (Stefig. 23, p. 38.) 



