Texas Hornshell (Popenaias popeii) is a large (shell length up to 10 cm) olive green to dark brown freshwater mussel that is distributed through the lower portions of the Pecos River and Rio Grande drainages In New Mexico, Texas, and Mexico. In New Mexico they are found in the Pecos River near Carlsbad. They inhabit various substrates in larger streams at the top and bottom of shallow, narrow runs. Appropriate host fish, which are unknown in New Mexico, are necessary for the survival of larvae.