Thesis (M.A.)--Boston University / The Atlantic species of the exocoetid genus Cypselurus are reviewed and six species recognized: Cypselurus comatus, C. cyanopterus, C. exsiliens, C. furcatus, C. heterurus, and C. pinnatibarbatus. Discussions of the ontogeny, diagnosis, and range of the genus are presented, along with a synonymy. Two keys to Atlantic species are presented; one for specimens under 100 mm SL. Characters distinguishing the species are: dorsal fin height and coloration; barbel number, shape, and length; anatomy and coloration of the pectoral and caudal fins; predorsal scale and vertebral count differences. For each species distinctive characters, description, and synonymy are given, and ontogeny, range, and reproductive biology are discussed. Satisfactory characters for distinguishing C. heterurus and C. furcatus are given for the first time. The validity of the synonymizing of C. leutkeni with C. heterurus and C. lineatus with C. pinnatibarbatus is upheld.