This short paper discusses two new synonyms of Ulnaria vitrea: Synedra mesocampa Brébisson in Kützing and Synedra tenuis Kützing. The data generated herein are based on original material and form a contribution to the taxonomic clarification of species in the genus Ulnaria. Both names discussed have barely been noticed since their original description and then usually considered as synonyms of Ulnaria ulna. Some additional notes on other relevant names are included, such as Synedra putealis O’Meara and Synedra tenuis var. subtilis (Kützing) Brun.