Of the key-shaped rings, several specimens of which have been preserved from Roman times, it has been suggested that the key projection was intended to serve as a guard for an exceptionally long finger-nail, similar to the finger-guards the Chinese wear for a like purpose. The fact that many of these key-rings are evidently too large to have been worn on the finger, makes it not improbable that the ring form was arbitrarily chosen, and that they may have been carried suspended from a girdle. Some of them, however, might have fitted on a very stout thumb, and a few of the rings of this type do not exceed the ordinary finger-ring in diameter.[120] One of the large and unwieldly Roman rings, or at least a ring made on this model, bears a bust said to be that of Plotina, the wife of Trajan. This was in the collection of Monsignor Piccolomini. The extraordinarily elaborate coiffure shows three rows of facetted gems, and this alone may be considered to testify against the antiquity of the ring. Still, even as a production of the Renaissance period, the fact that it at least figures an ancient form makes it an object of interest and of a certain archæological value.[121] It was in the late Republican, and especially in the Imperial age in Rome, that the greatest variety of ring forms were produced, originally influenced by the earlier Etruscan art, and later largely by the extraordinary eclectic art of Alexandria, where the combination of Egyptian, Oriental and Greek elements brought forth many peculiar forms, some of which are noted elsewhere. A Romano-Egyptian ring has a flat hoop, sub-angular on the outside, the large circular bezel being engraved with three figures of divinities. Then there are the composite rings, sometimes having as many as four hoops, joined together at the back of the bezel. A striking type is the penannular ring in the form of a coiled serpent, or else having at each extremity the head of a serpent. In another form the bezel is lozenge-shaped. There are also massive rings with an elliptical hoop and thick projecting shoulders, the setting being depressed; sometimes the shoulders slope sharply up to the bezel, forming a decided angle on the hoop. Hoops polygonal on the outside and circular within also occur. Some twin rings were made adapted to fit on two fingers of the hand; in one of these are three cup settings holding garnets, one on the top of each hoop and one between the hoops. In some instances the hoops of these twin rings were not closely joined to each other, but connected by a short gold chain, so that the rings could either be worn on a single finger, or on two fingers. [Illustration: Gold ring with plain hoop on which is freely looped a little mouse wrought in gold and white enamel. It slips around the hoop. About 1600 Albert Figdor Collection, Vienna]