PEARLS AND PEARL FISHERIES. 
377 
As many as a hundred small pearls have been found in a single shell, but as a 
rule these have little or no value. Very curious nacreous groups made of many small 
pieces are at times found attached to the hinge, but these are generally without 
sufficient luster to be of value, and are rarely collected. These groups are caused 
by the conglomeration of many small pearls cemented by a deposit of nacre, and are 
often half an inch across. 
The same causes and operations that result in the production of pearls also 
produce in a modified way the tuberculose or knob-like protuberances and irregularities 
of surface that are frequently seen on the pearly inner faces of the valves and pro- 
jecting therefrom. The flatter or less pronounced form of these nacreous excrescences 
are often called “blister pearls,” because of their resemblance to vesicular eruptions 
or to water-blisters caused by burns. 
When the growth of the pearl is abnormally strong, the pressure which it exerts on 
the outer wall of this tissue pocket becomes so powerful that the pocket is absorbed 
on the side toward the shell, bringing the hard pearl directly against the latter. It 
then becomes impossible for the pearl to grow any more at the point of contact, for 
there is no tissue to secrete the lime substance; but it grows on the rest of the surface, 
and the thickening layers, as they are formed, pass directly into the nacre layers on 
the inside of the shell and thicken the shell itself. Through these overlayers the 
pearl is connected with the shell as though by different layers of covering cloths. At 
first it clings to the shell at one point only, afterwards enlarging the area of its adhe- 
sion. In this manner twin or united pearls are formed. 
All these varied kinds are found in the marine pearl oysters as well; but the 
fresh-water mollusks have the additional beauty of great variety of tints and of 
partial transparency in their nacre. In color the Unio pearls present an extended 
series of shades from dead opaque white, having but little value, through various 
tints of pink, yellow, and salmon, or a faint purple, passing to a bright red so closely 
resembling a drop of molten copper as almost to deceive the eye. Some are very light 
green and brown, others rose-color, and still others are pale steel-blue, russet, and 
purplish-brown. In addition to their color and luster, they are beautifully iridescent. 
The white and the pink pearls are exceedingly handsome, and the finest, owing to 
their delicate sheen or layers, are at times more lustrous than even the best oriental 
pearls. This luster is increased by their greater transparency, and a really fine white, 
pink, yellow, or iridescent pearl is often quite translucent. They are found also in 
many odd and remarkable shapes. 
Elongated fish-like forms found near the hinge of the shell and called hinge 
baroque pearls are abundant. Others, with a slight addition of gold and enamel, 
may be made to represent human and animal heads, bat and bird wiugs, and similar 
objects. Mallet-shaped pearls are found with fine color and luster at each end, though 
generally with opaque sides; also, grouped or bunched masses of the pearly nacre, 
made up of from one to over one hundred distinct pearls in fanciful shapes, are of 
occasional occurrence. Feather-like forms with curiously raised points and an odd 
rounded variety with raised pitted markings are quite abundant. A pearl was 
mounted in this country that strikingly resembled the bust of Michael Angelo; and 
a number of unique designs have been made of baroques, similar to those mounted 
by Dinglinger and exhibited in the Green Vaults at Dresden. Although the pearls 
used here have not been as large as those shown in Dresden, greater taste has been 
employed in mounting them. The variety of the Unio forms being so great, an artist 
