The Tritons have the following appearance. On their heads they grow hair like that of marsh frogs not only in color, but also in the impossibility of separating one hair from another. The rest of their body is rough with fine scales just as is the shark. Under their ears they have gills and a man's nose; but the mouth is broader and the teeth are those of a beast. Their eyes seem to me blue, and they have hands, fingers, and nails like the shells of the murex. Under the breast and belly is a tail like a dolphin's instead of feet.
Pausanius, Description of Greece, 9.21.2

A deputation of persons from Olisipo, that had been sent for the purpose, brought word to the Emperor Tiberius that a triton had been both seen and heard in a certain cavern, blowing a conch-shell, and of the form under which they are usually represented. Nor yet is the figure generally attributed to the nereids at all a fiction; only in them, the portion of the body that resembles the human figure is still rough all over with scales. For one of these creatures was seen upon the same shores, and as it died, its plaintive murmurs were heard even by the inhabitants at a distance.
Pliny, Historia Naturalis, 36.4