Arkansia
Arkansia is a monotypic genus of freshwater mussels in the family Unionidae, the river mussels. The sole species in the genus is Arkansia wheeleri. Its common names are the Ouachita rock pocketbook and Wheeler's pearly mussel. The genus was named for the state of Arkansas, where the mussel was first discovered. This is a federally listed endangered species of the United States. Distribution. This species is native to Arkansas, Oklahoma, and Texas in the United States, which have only four or five small, isolated populations. Of the remaining populations, only the one located in the Kiamichi River in  Oklahoma is viable. Description. This mussel is not sexually dimorphic; the sexes appear the same. The shell is somewhat rounded or oval, up to 11.2 centimeters long by 6 wide by 8.7 high. The shell is brown or black, lustrous and iridescent. The nacre is part pink and part white or bluish.