AVICULIDiB. 271 



ELECTROMA, Stolicz. Oblique, thin, mostl^^ smooth ; iueqaivalve, 

 the right valve being somewhat flatter; the hinge-line is shoi't, and 

 the posterior wing very short ; not separated from the body oi" 

 the shell. ^4. smaragdina^ Reeve. 



PSEUDOPTERA, Meek. Shell more or less obliquely subtrigonal 

 or subovate ; hinge short, compressed ; anterior wing short, not 

 defined ; posterior abbreviated, compressed, and nearly or quite 

 without any marginal sinuosity below it; anterior margins some- 

 times a little sinuous near the middle, but without any byssal 

 sinus under the anterior wing. Avicula anomala^ Sby. (cxxx, 

 38). Pinna fibrosa, M. and H. Cretaceous. 



OXYTOMA, Meek. Shell with nearly the general outline of the 

 tj'pical form, but usually less oblique, and more inequivalve, with 

 the byssal sinus very decpl.y and sharply cut, close up under the 

 anterior auricle of the right valve. Several sp. Triassic, Jurassic 

 and Cretaceous. Avicula Manateri, Bronn. 



MELEAGRiNA, Lam., 1799. (Margaritophora, Muhlfeldt. Per- 

 lamater, Schum., 1817.) The "pearl-oysters" are less oblique 

 than the otiier Aviculse, and their valves are flatter and nearly 

 equal; the posterior pedal impression is blended with that of 

 the great adductor. Animal with mantle-lobes united at one 

 point b}' the gills, their margins fringed and furnished with a 

 pendent curtain; curtains fringed in the branchial region, plain 

 behind ; foot finger-like, grooved ; byssus often solid, cylindrical, 

 with an expanded termination ; pedal muscles four, posterior 

 large in front of the adductor ; adductor composed of two 

 elements ;. retractors of the mantle forming a series of dots, and 

 a large spot near the adductor; lips simple; palpi truncated; 

 gills equal, crescentic, united behind the foot. Pearl-oysters are 

 found at Madagascar, Ce3don, Swan River, Panama, etc. Manilla 

 is the chief port to which they are taken. There are three prin- 

 cipal kinds, which are worth from £2 to £4 per cwt. : 1. The 

 silver-lipped, from the Society Islands, of which about twenty 

 tons are annually imported to Liverpool. 2. The black-lipped, 

 from Manilla, of which thirty tons were imported in 1851. 3. A 

 smaller sort from Panama, 200 tons of which are annually 

 imported; in 1851 a single vessel bi'ought 340 tons. — T. C. 

 Archer. These shells afl'ord the " mother-o'-pearl " used for 

 ornamental purposes ; and the " oriental " pearls of commerce. 

 Mr. Hope's pearl, said to be the largest known, measures two 

 inches long, four round, and weighs 1800 grains. Pearl-03'sters 

 are found in about 12 fathoms water ; the fisheries of the Persian 

 Gulf and Ceylon have been celebrated from the time of Plin3^ 

 M. margaritifera^ Linn, (cxxxi, 63,'. 



AUCELLA, Keyserling, 1846. Very inequivalve; left umbo 

 prominent, earless ; right valve small and flat, with a deep sinus 

 beneath the small anterior ear. Fossil, 4 sp. Permian — Gault; 



