The harpacticoid copepod subfamily Thompsonulinae Lang, 1944, formerly recognized as belonging to the family Tachidiidae (Lang, 1948) is raised to family rank and redefined to include only the genera Thompsonula T. Scott and Caribbula gen. nov. Thompsonula hyaenae (I. C. Thompson) and T. curticauda (Wilson) are redescribed and refigured. Re-examination of the original material showed that Wilson's Rathbunula agilis is synonymous with T. curticauda and not with T. hyaenae, as suggested by Lang (1948). It is now clear that the two species of Thompsonula have distinct distributions, T. curticauda being confined to the North American continent and T. hyaenae to western Europe and the Mediterranean. The genus Caribbula is established to accommodate the type species, T. hyaenae elongata (Gee) and C. fleegeri sp. nov. which are described and figured. The genus Caribbula is distinguished from Thompsonua, primarily by the unique sexual dimorphism on the exopod of P4 and, at present, is known only from the eastern seaboard of the United States and Gulf of Mexico. The genera Danielssenia, Psammis, Paradanielssenia, Micropsammis and Leptotachidia are tentatively assigned to the family Paranannopidae Por.