The lineid heteronemertean nominal species Borlasia viridis Quoy & Gaimard, 1833 (type locality: Port Jackson, Sydney) has been considered synonymous with Borlasia tricuspidata Quoy & Gaimard, 1833 (type locality: Guam) and referred to as Notospermus tricuspidatus (Quoy & Gaimard, 1833). The species eventually published in 1833 as Borlasia viridis had been quoted as Ophiocephalus viridis in Blainville's 1828 work, with the taxonomic authority ascribed to Quoy & Gaimard. As O. viridis (= B. viridis) and B. tricuspidata are here interpreted as different species, the former is validated as Notospermus viridis (Quoy & Gaimard in Blainville, 1828) comb. nov. The generic name Ophiocephalus Quoy & Gaimard in Blainville, 1828 has not been used as valid after 1899 for nemerteans (not as incorrect subsequent spelling of the freshwater perciform fish genus Ophicephalus Bloch, 1793), while Notospermus Huschke, 1830 has been used in at least 31 works published by 24 first authors from 1991 until 2026, thus satisfying the conditions stipulated in Article 23.9.1 of the International Code of Zoological Nomenclature (4th edition). Notospermus is here declared a nomen protectum with respect to Ophiocephalus, a nomen oblitum.