CLASS V. LAMELLLBRANCHIATA: ORDER 2. ASIPHONATA. 523 



ORDER 2. ASIPHONATA. 



This term, derived from the Greek, signifies without tube, and includes 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 fresh-water, and few of our lakes, 

 jionds, 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 with 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. elonyata is found in Great 

 Britain, and formerly produced numerous 

 pearls ; these were fjimous even in the time 

 of Julius Caesar. In Ireland and Scotland 

 this species has produced pearls, in modern 

 times, valued at from twenty to four hund- 

 red dollars. 



The U. JVovi-eboraci, found in the State 

 of New York, resembles the U. pictorum. 

 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- 

 land, has largely contributed to our knowledge of subjects 

 connected with the natural history of the LTnited 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 thousand young animals, with their shells 

 perfectly formed, both valves being distinctly visible by the 

 microscope ! 



Pearls have becTi 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 Brook, near the town 

 of Patterson, a shoemaker by the name of Ilowell, found a 

 few years since a pearl of enormous size in a mussel, but, un- 

 THE UNIO SPINOSA. fortunatcly, not till after it had been cooked, by which means 



it was ruined. About this time, that is, in 1857, a carpenter of Patterson, named Quackenbush, 



THE UNIO ELONGATA. 



