As a result of an examination of the original material of G. O. Sars and of new material from Björnehodebukta, Oslofjord,Danielssenia fusiformis(Brady) is synonymized withDanielssenia typicaBoeck and the latter species redescribed. Two new species are described;D. quadriseta, from Oslofjord, is distinguished from all other known species by the presence of only 1 inner seta on the distal endopodite segment of swimming leg 3;Danielssenia reducta, from Alaska, is the only species in the genus with just 3 setae on the terminal endopodite segment of swimming leg 4. A new key to species ofDanielsseniais also provided