Five new species, referred to the genera Schistomeringos and Ophryotrocha, are described: S. eliasoni and S. subaequalis from Öresund, Denmark, and S. nigridentata, S. macilenta, and O. lobifera from Lindåspollene, western Norway. Based on types and new material an extended description of the northeastern American Schistomeringos caeca (Webster & Benedict) is given; a sympatric species from eastern Canada is with doubt referred to S. eliasoni. The material of ?Stauronereis furcata Eliason (not Hartman) has been reexamined; it consists of three species, one of which is referred to S. eliasoni, and two of which are indeterminable.
All species except O. lobifera have subbiramous parapodia and furcate setae with long tines; the species are mainly separated on parapodial characters and morphology of jaw parts. Especially large species differences which may prove of generic importance pertain to the jaw parts, and their importance for species discrimination is stressed.
Presence of furcate setae is inconsistent in S. eliasoni and S. subaequalis as some specimens lack furcate setae. Long additional setae have been noted in three species, and double maxillary parts, indicating maxillary replacement, in four species.