CLASS V. LAMELLIBRANCHIATA: ORDER 2. ASIPHONATA. 523 
ORDER 2. ASIPHONATA. 
THE UNIO PICrORDM. 
This term, derived from the Greek, signifies without tube, and inckides some of the most im- 
portant of molluscous animals. In general, the shells are more or less orbicular, and the valves 
often unequal. The animal reposes on and adheres by the more convex of its valves. The 
mantle is open throughout ; the foot is sometimes absent ; when present it is small and usually 
furnished with a byssus ; there is only a single adductor muscle. The order includes several 
families. 
THE UNIONACEA. 
This family includes numerous species, two hundred of which belong to the United States, 
where they are called Fresh-Water Clams 
and Mussels. They are, in fact, all inhab- 
itants of fi'esh-water, and few of our lakes, 
ponds, or rivers are without some of the 
species. From the observations of Dr. 
Kirtland and others, it appears that they 
are bisexual. They have an equivalve shell, 
covered Avith a smooth epidermis, and lined 
with pearly matter. Several of the species 
furnish pearls of an inferior quality. The 
Unio pictorum is common in Europe, and 
derived its name from the fact that its shell 
was formerly used by painters to hold their 
colors. The U. elongata is found in Great 
Britain, and formerly produced numerous 
pearls ; these were famous even in the time 
of Julius Csesar. In Ireland and Scotland 
this species has produced pearls, in modern 
times, valued at from twenty to four hund- 
red dollars. 
The U. Novi-ehoraci, found in the State 
of New York, resembles the U. j^ictoruni. 
The U. cariosa, found in the Hudson and 
Passaic Rivers, is one of the largest and most beautiful species. The U. spinosa is found in the 
Mississippi River. The U. radiata is common in the Middle 
^ States. Dr. Lea, of Philadelphia, who, as well as Dr. Kirt- 
^^t- V^^^^Mk ^^^^^ ^^^s largely contributed to our knowledge of subjects 
>^^>">x^'^A'^''«!'^^Bv connected with the natural history of the United States, has 
furnished some extremely curious facts in relation to the 
Anodonta undulata, belonging to this family. This species, 
which is three inches long, he found to be hermaphrodite 
and viviparous ; on dissection, he discovered the oviducts to 
contain six hundred thousaiid young animals, with their shells 
perfectly formed, both valves being distinctly visible by the 
THE UNIO ELONGATA. 
microscope 
Pearls have been occasionally found in the mussels of the 
rivers of Connecticut, New York, and New Jersey. In a small 
stream of the latter state, called Notch Brooh, near the town 
of Patterson, a shoemaker by the name of Howell, found a 
few years since a pearl of enormous size in a mussel, but, un- 
fortunately, not till after it had been cooked, by which means 
it was ruined. About this time, that is, in 185*7, a carpenter of Patterson, named Quackenbush, 
THE UNIO SPINOSA. 
