Gérard Paul Deshayes was a French geologist and conchologist.
He was born in Nancy, his father at that time being professor of experimental physics in the École Centrale of the département Meurthe
He studied medicine in Strasbourg, and afterwards took the degree of bachelier ès lettres in Paris in 1821; but he abandoned the medical profession in order to devote himself to natural history. For some time he gave private lessons on geology, and subsequently became professor of natural history in the Museum d'Histoire Naturelle.
He was distinguished for his researches on the fossil mollusca of the Paris Basin and of other areas Cenozoic cover. His studies on the relations of the fossil to the recent species led him as early as 1829 to conclusions somewhat similar to those arrived at by Lyell, to whom Deshayes rendered much assistance in connection with the classification of the, then, Tertiary system into Eocene, Miocene and Pliocene.
With André Étienne d'Audebert de Férussac, he co-authored an important study on terrestrial and river mollusks titled Histoire naturelle générale et particulière des Mollusques terrestres et fluviatiles.