The polyplacophoran genus Hanleya contains two similar species in the Northeast Atlantic, H. hanleyi (Bean in Thorpe, 1844) and H. nagelfar (Lovén, 1846), which were primarily differentiated by dramatic difference in size but also in part by distribution and minor morphological and ecological features. The question of whether these two names represent two species or whether H. nagelfar is merely a name for H. hanleyi that have grown to extraordinary size, has been raised repeatedly since 1865. The problem was protracted by inaccessibility of the type specimen for the senior species name, and a lack of material collected near the type locality of H. hanleyi, both issues which we resolved in the course of this study. We examined the details of valves, girdle armature, and radula in specimens of Hanleya hanleyi from the Mediterranean Sea and Scotland. The similarity of relevant features among small specimens of H. hanleyi and H. nagelfar from Scotland, the Mediterranean Sea, Norway and Newfoundland Bank and the type specimen of Hanleya hanleyi suggests the two species are synonymous. Hanleya nagelfar is a junior synonym of H. hanleyi. Finally we note the eggs of H. hanleyi contain an unusual large drop of lipid that may increase their floatation. We propose that the eggs and larvae of H. hanleyi have an extended pelagic distribution and this extended dispersal period may connect populations from bathyal habitats in the slope of Newfoundland Bank via surface currents of the Gulf Stream System to northward and eastward in the Atlantic ocean.