The finest examples of these brooches are preserved in the museum of the Royal Irish Academy in Dublin, the National Museum of Antiquities of Scotland in Edinburgh, and the British Museum. Among the earliest--which are not, however, prior to the later Anglo-Saxon period, and make their appearance about the ninth century--are those with a plain penannular ring, formed of a solid cylindrical rod of silver, terminating with bulbous knobs furnished with expansions, and often covered with a peculiar prickly ornamentation like thistle-heads. Specimens of this style of brooch have been found in Ireland, Scotland, and in the north of England. The simplest of the silver penannular brooches with discoidal terminations in the museum at Edinburgh is one from Croy in Inverness-shire. It has ends expanding into circular discs with amber settings. The most elaborate, one of two known as the Cadboll brooches, found at Rogart in Sutherlandshire, has four raised heads of birds, two upon the circumference of each disc, and two upon the ring. The collection in the Royal Irish Academy contains several splendid brooches of a similar type, notably the Kilmainham brooch from Kilmainham, Co. Dublin, the surface of which is ornamented with compartments of thin plates of gold tooled with interlaced patterns. The terminations of the penannular ring soon become so expanded that they fill up exactly half the ring. Upon these flattened plaques, which have just space enough between them for the pin to pass, a serpent or dragon form is a frequent ornament, as well as the intertwined triple ornament, or _triquetra_, while the surface is set at intervals with bosses of amber. The most remarkable examples of this type are the University brooch in the collection of Trinity College, Dublin, and the Clarendon brooch found in Co. Kilkenny, and now in the museum of the Royal Irish Academy.