The Efficiency of Flotation Compared with Other Methods for Recovering Assemblages of Terrestrial and Aquatic Gastropods from Archaeological Deposits, with Reference to the Site of Pico Ramos (Basque Country, Spain)

We analysed assemblages of shells of land snails and small aquatic and wetland gastropods from a late Mesolithic-early Neolithic deposit in the cave of Pico Ramos (Basque Country). Shells were recovered by hand during excavation and all excavated deposit was processed by flotation, with a 250 μm mesh to recover floating material and a 1.0 mm mesh to recover the heavy fraction. The total assemblage comprised 5780 individuals (MNI) among 33 taxa, the sieved sub-assemblage having the highest proportions of these (2841 MNI in 31 taxa) and the hand-picked sub-assemblage the lowest (698 MNI in 11 taxa). Eleven taxa were absent from the flotation sub-assemblage, although the recovered MNI (2241; 39% of the total MNI) was high. The palaeoecological implications of the results are considered. Adult and large-sized juvenile shells of the edible land snail Cepaea nemoralis are abundant in the hand-picked sub-assemblage, but it is the absence of small-sized juvenile shells in the flotation and wet-sieved sub-assemblages that permits the inference that the species was collected for consumption. Wet sieving is therefore essential, both for interpreting hand-picked samples and in particular for the recovery of representative assemblages of land molluscs.