The northern riffleshell is a small to medium size (up to 3 inches long) freshwater mussel that was listed as endangered, without critical habitat, in 1993 (58 FR 5638-5642). Its shell exterior is brownish yellow to yellowish green with fine green rays. The shell interior is typically white. The species is sexually dimorphic; male shells are irregular ovate in outline, with a wide shallow sulcus just anterior to the posterior ridge. Female shells are obovate in outline, and greatly expanded post ventrally. The expanded shell shape of the female riffleshell results from shell growth around the expanded marsupial region.