Etruscan rings assume various characteristic and peculiar forms, many of which are found among the Roman rings of a later period, indicating the derivation from the Etruscans of ring-wearing among the Romans. One of these in the British Museum has a broad hoop ending in convex shields, a scarab being pivoted in the terminals; in others, the hoop is hollow, terminating in cylindrical ornaments, between these a scarab revolves on a wire swivel. A peculiar example has a grooved hoop, the ends being convex disks, in which is pivoted a scarab. One of these Etruscan rings has a very large convex oval bezel, around the slope of which run a series of embossed figures. As an example of Roman art found in Egypt, we have a spiral ring of serpent form, either extremity terminating in a bust, of Isis and Serapis respectively. The conjecture has been made that this ring, and others of the type, may have been intended to figure the reigning emperor and empress of Rome under the types of Isis and of Serapis, the latter a Græco-Egyptian divinity as worshipped in Alexandria and in the Roman world, though having a distinctly Egyptian form in the national pantheon as Asar-Hapi, or Osiris-Apis. The rings of the type described have the advantage of being easily adapted to a finger of any size, since pressure at both extremities would enlarge the girth of the single spiral.[118] In his Etymologiæ, Isidore of Seville defines three of the types of rings worn in ancient times, the _ungulus_, the _Samothracius_ and the _thynnius_.[119] The _ungulus_ was set with a gem and owed its designation to the fancy that the stone was as closely attached to the gold of the ring as a human nail (_ungulus_) was to the flesh of the finger. The Samothracian ring was of gold, but had an iron setting. Lucretius in the sixth book of his great philosophic and scientific poem, “De Natura Rerum,” in speaking of the magnet to which he attributes negative and positive powers, of repulsion and of attraction, relates that when, in an experiment, Samothracian rings were placed in a brazen dish beneath which a piece of magnetic iron was moved to and fro, he had seen the rings leap up, as though to flee from an enemy. The third type of ring was the _thynnius_, the name indicating, according to Isidore, that it was made in Bithynia, called at an earlier time, Thynna. Horace writes, in one of his odes, of rings “chased by a Thynnian graver.”