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Abstract. The variability of the reticulum pattern, ornamentation and outline of the Urocythereis populations of the la strea Bay is analysed. The results show that the shell features of the form U. distinguenda (Neviani, 1928) (= U. oblonga Brady, 1866) have to be included within the high variability range of U. margaritifera (G.W. Müller, 1894). Consequently, it is suggested that in the upper infralittoral waters of the inlet two (and not three, as stated in previous investigations) species of the genus Urocythereis presently live. A second form, displaying a relatively low variability, is described as a new species, U. ilariae sp. nov.