Chesapeake Bay specimens ofAcartia, identified by C. B. Wilson asA. clausii andA. longiremis, were re-examined. All the specimens identified asA. longiremis and most of those labelledA. clausii wereA. tonsa. A. clausii was present only in two winter samples. The postulated change in the composition of species ofAcartia in the Bay can no longer be supported, since it arose from Wilson's misidentifications.