World Polychaeta Database (WPolyD). There are no figures and the brief descriptions may be preliminary, but no later article was published (Stimpson's materials & MS are said to be destroyed by fire in 1871). Date of publication used in literature is either 1855 (the part date) or 1856 (the volume date). The correct date is 1855, the part date, according to Manning (1993), but without detailing his evidence for this. Late 1855 is the best date achievable from study of the part dates sequence in a 1913 index to the journal (qv). As well as the version in volume 10 of the Proceedings, BHL also has an undated unpaginated separate as a 'book' ( https://doi.org/10.5962/bhl.title.51445 )