''Arcidens confragosus'' is a species of

freshwater mussel Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails. The majority of bivalve molluscs are saltwater species that l ...

s in the family

Unionidae The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is a ...

, the river mussels. It is commonly known as the rock pocketbook, but also has many other common names: bastard, black pocketbook, grandmaw, queen, and rockshell.

Distribution

This species is widespread in central parts of the United States: it occurs in the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

drainage and in coastal rivers draining to the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, from the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

in Texas east to the

Mobile River The Mobile River is located in southern Alabama in the United States. Formed out of the confluence of the Tombigbee and Alabama rivers, the approximately river drains an area of of Alabama, with a watershed extending into Mississippi, Georg ...

System in Alabama.

Description

The shell is "" or pear-shaped, heavily sculptured, but fairly thin, up to long. The shell is green to dark brown. The

nacre Nacre ( , ), also known as mother-of-pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer. It is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...

is white,

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstruc ...

References

Unionidae Bivalves of North America Freshwater animals of North America Endemic molluscs of the United States Molluscs described in 1829 Taxa named by Thomas Say {{Unionidae-stub