A very curious hitherto unknown monstruosity of Neptunea antiqua (L.), figured in this article, was found in July of the year 1930 by C. H. M. Nauta on the beach near Wassenaarse Slag in the province of Zuid-Holland. The specimen is preserved in our collection. This monstruosity finds its place among other such forms, treated by Jeffreys and is named by me: monstr. uncinata nov. monstr. It differs from typical specimens of the species by its striking base, which is not produced but quite rounded, the siphonal canal thus turned very manifestly to the left and running nearly horizontal. This canal is not unlike the one found in some species of the genus Cerithium, e.g. Cerithium vertagus (L.), even accepted as a distinct genus Vertagus Schumacher by Dautzenberg. The monstruosity varicosa Jeffreys is, as explained in this article, a common phenomenon in Neptunea antiqua caused by the fact that after reaching maturity, a specimen with expanded lip, grows further and produces after a short period another reflected lip, without having the possibility to resolve the former reflected outer lip, which remains visible on the last whorl as a varix. It even occurs that many such varices are to be seen, close together and separated only by deep grooves, commonly at the end of the last whorl.