Pliny the Elder [1st century CE] (Natural History, Book 9, 51): In the same family are water and land snails, that protrude out of their abode and shoot out and draw in two horns as it were. They have no eyes, and consequently explore the way in front of them with their little horns. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.29; Worms 9.47): [Thomas describes the snail under the names coclee and testudo vermis, and as both a a fish and a worm.[ [Fish 7.29] Snails [cochlee], both aquatic and terrestrial, move to support themselves by extending and contracting their two horns. They lack eyes, but nature has given them limbs for the dimmed lights. And so they are said to travel with their horns, and are not deceived, wherever they desire to step. Snails and oysters and every kind of them increase and decrease according to the moon. For as the scientists say, when the moon is waxing, it increases the moisture; but when it is in deficiency, the humors are diminished. [Worms 9.47] The snail [testudo vermis, "tortoise worm"] comes about from the decay of the grass during the very wet and hot season. The animal is slow and thick, with much fat. Some are red, some white, some black, some crimson, according to the changes and corruptions of the air. It forms a house for itself in a wonderful manner, covered in a shell of bony or rather marble substance; and this is strange: for it makes a dwelling for itself out of saliva, which is slippery and thick, and by the heat of the sun it gradually hardens in a certain way into a stone. [Thomas here quotes from Ambrose (Book 6, 4.19), who is actually describing the tortoise, not the snail.] This, as the blessed Ambrose relates, when it has eaten the entrails of a snake, and it notices the poison creeping into it, it exercises the medicine of its salvation with oregano [or marjoram]: and, although it is in the water of swamps, it nevertheless knows how to treat itself with its own antidote, and with certain help it proves itself to know the healing powers of herbs. If you throw salt over it, almost all of it will melt into nothing, and you will scarcely find anything of it but a scrap. This worm is useful for medicine. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.106): A Snayle is called Testudo, and is a worme, and hath that name, for he is healed in is house, as in a chamber, as Isid[ore] saith li. 12. And there are foure maner of snailes, land snailes, & sea stronde snailes, & fennie snailes that lye in mareyes, and river snailes, and some men suppose though it be not to be beléeved, that the ship goeth slower, if he beareth the right foote of the snaile, as Isi[dore] sayeth lib. 12. De Testudine autem quaere supra, in litera L. de Limace. - [Batman]