The ariid Notarius grandicassis (Valenciennes, 1840), commonly known as Thomas sea catfish, occurs at northeastern South America, ranging between Colombia and Brasil. It was reported originally from the mouth of the Amazon to the Golfo de Venezuela. In 2002, it was reported from the Colombian Guajira peninsula. Herein, we report the species from the mouth of the Magdalena River (Bocas de Ceniza), where it is rather frequently obtained by fishermen.