Image of Arcidens confragosus (Say 1829)

Description:

This shell had me confused, as it looks like a big, inflated Quadrula nobilis. Until I saw the interior, that is. It is very different in outline from specimens of A. confragosus found in other parts of Texas, but looks very much like some specimens from the upper Mississippi drainage. It might have been a hitchhiker on a fish that was stocked in Lake Corpus Christi. 118mm Knobs on beak are alternating like Obliquaria reflexa. I've only seen this on these two species and juvenile specimens of Plectomerus dombeyanus.