The same idea is developed in a slightly different way by Firmicus Maternus (8, 15, 1):
In primis partibus Capricorni oritur Ophiuchus. Hoc sidere oriente qui nati fuerunt, erunt Marsi qui pestiferos angues sopitis ac mitigatis aculeis mitigent. Si vero hoc sidus in occasu fuerit inventum, et hunc locum . . . respexerit, venenati serpentis ictu morientur.
Thus it is likely that the amulets bearing this design were believed to give protection against poisonous snakes. It is true that Ophiuchus was sometimes taken as a type of Christ, according to a Gnostic notion which may have been based upon and ultimately interpolated into the ancient commentary on Aratus:24
δευτέρα δὲ κτίσις ἐστὶν ἡ κατὰ Χριστόν, δι᾿ ἧς ἀναγεννώμεθα, ὅ ἐστιν ὁ Ὀφιοῦχος ἀνταγωνιζόμενος τῷ θηρίῳ καὶ κωλύων ἐπὶ τὸν στέφανον έλθεῖν τὸν ἡτοιμασμένον τῷ ἀνθρώπῳ: “There is a second creation, through which we are regenerated, the creation according to Christ; who is the Serpent-Holder, who strives with the creature and keeps him from reaching the crown prepared for Man.” But in the absence of any distinctive Christian symbol, the practical explanation of the design as a charm against snakes is to be preferred.
Representations of Sarapis seated upon his throne are common, and the majority of those seen on magical stones differ little from the types used on coins or on nonmagical gems. There is one striking and elaborate type which, to the best of my knowledge, has been published only once, and that with a faulty and misleading illustration and description. Dismissing that for the moment, we consider first the largest and best-preserved of a series of six stones; it is in the Brummer collection. (D. 354)
It is an oval dark green jasper with red spots (bloodstone), larger than most gem amulets (42 X 32 X 5 mm.). Sarapis sits enthroned facing left, his right hand extended, his left resting on a tall scepter which has a bird, apparently an ibis, on its top.25
Under the throne is a crocodile, under the crocodile a mummy resting on the back of a lion, which seems to be walking to left. A scarab with extended wings is over the head of Sarapis, a scorpion just under his outstretched right hand. This design is enclosed by a serpent; not, however, the common ouroboros, but a serpent with radiate human head, which is turned inward to face Saraρis. Round the edge of the stone, outside the serpent, is the long palindrome beginning Iaeobaphrenemoun. The reverse design is Harpocrates seated on the lotus; in the field are a star, a crescent, and several characters. On the bevel are the word Iao
and the vowels arranged in pyramid order, that is, one alpha, two epsilons, and so
24 Hippol. Refut. 4, 48, 7 (p. 71, 23–26, ed. Wendland).
25 In P. Lond. 46, 446ff. (PGM V), directions ate given for engraving an iaspachates with a figure of Sarapis enthroned, holding a royal scepter with an ibis on top. Nothing is said of the other features of the type discussed in the text — scorpion, crocodile, mummy, etc.