The analysis of shell deposits eroded by a ebb-tide channel on Saltes Island (Tinto-Odiel estuary, SW Spain) resulted in the identification of a new shell midden, associated with the activity of a nearby Roman factory over the 4th-5th centuries CE. This midden differs from other old shell deposits (sandy tidal flats, cheniers, washover fans) in several features: a) its malacological content, dominated by edible species (mainly the bivalve Glycymeris nummaria) and differentiated by statistical analysis; b) a partial selection and better conservation of Glycymeris nummaria (Linnaeus), its most abundant species; c) the absence of microfauna, which implies a previous washing to its final deposit; and d) an age concordant with the one deduced from the Roman amphoraic remains found in this area and subsequent to the washover fans on whom it was deposited. All these features, together with the absence of both anthropic fractures or cooking, would indicate that this Roman shell midden was the end result of a trawling on subtidal Glycymeris-rich sandy bottoms with adjacent grasslands, where the gastropod Bittium reticulatum (da Costa) was the most abundant mollusc. This gastropod is the dominant species in the remaining shell deposits.