AVICULID.A. areal 
ELECTROMA, Stolicz. Oblique, thin, mostly smooth; inequivalve, 
the r:ght valve being somewhat flatter; the hinge-line is short, and 
the posterior wing very short; not separated from the body of 
the shell. A. 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. Alvicula anomala, Sby. (exxx, 
38). Pinna fibrosa, M.and H. Cretaceous. 
oxytToMA, Meek. Shell with nearly the general outline of the 
typical form, but usually less oblique, and more inequivalve, with 
the byssal sinus very deeply and sharply cut, close up under the 
anterior auricle of the right valve. Severalsp. Triassic, Jurassic 
and Cretaceous. Avicula Munsteri, Bronn. 
MELEAGRINA, Lam., 1799. (Marg aritophora, Muhifeldt.  Per- 
lamater, Schum., 1817.) The “pearl-oysters” are less oblique 
than the other Aviculez, 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 by 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 s;ot near the adductor; lips simple; palpi truncated ; 
gills equal, crescentic, united behind the foot. Pearl-oysters are 
found at Madagascar , Ceylon, Swan River, Panama, ete. 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 Liv erpool. 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 mescel brought 340 tons.—T. C. 
Ancuer. These shells afford 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-oysters 
are found in about 12 fathoms water; the fisheries of the Persian 
Gulf and Ceylon have been celebrated from the time of Pliny. 
M. margaritifera, Linn. (exxxi, 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; 
