studies.14 In summary, it can be said that there is sufficient agreement between them to indicate that the form r(h)ymi is related to the stem of the Welsh word rhwmp, in the words of Sir Ifor Williams, 'a carpenter's tool to make holes in wood, gimlet', and he makes a comparison with the river-name Taradr, which is another Welsh word of similar meaning, 'auger'. The realistic assumption is that these rivers were so named because they bored and rutted their way through the land, others being named after animals which have a similar habit, like Twrch (W twrch 'wild boar'), Banw (W banw 'pig, piglet) cf. Banff in Scotland, Gwys (W gwys 'pig') etc. Further, the special toponymical feature of the valley is that at its higher and lower ends there are two places which both bear the name of the river, one much older than the other. On the eastern outskirts of Cardiff in an area which was once in Gwynllwg but is now within the limits of the city and was identifiable as the manor of Rhymni, the church was named by reference to its location by the river. This is recorded in the well-known ecclesiastical valuations of 1254 and c. 1291 as Ecclesia de Renny and Rempney respectively15 and it later became the centre of the parish of Rhymni (Rumney). For all practical purposes the parish was coterminous with the manor of the same name, and the castle of Rhymni is recorded by the beginning of the fifteenth century.16 The manor also had its great house, Llanrumney Hall, the home of a branch of the Morgan family of Tredegar House, on the parkland of which the present suburb of Llanrumney came into existence and was in turn brought within the Cardiff city boundary in 1951. In this name, the prefix llan- is not what it appears to be, namely that which signifies 'enclosure, cell, church', but W glan 'bank, shore' + the river-name Rhymni in reference to the location. *Glanrhymni became *Lanrhymni by lenition of the initial consonant after those Welsh prepositions most frequently used with Welsh place-names in common parlance, i 'to' and o 'from', and after a period of usage during which the lenited form gained currency17 it was erroneously restored to what was considered to be the 'correct' form, Llanrhymni (Llanrumney). This particular substitution of elements occurs with a frequency which can almost be termed common, and further examples in this area will be noted infra.1* However, where the manor is in question, its original name was that of the settlement of Tredelerch (Tredelerch 1536-9, Tref Delerch 1606, Tredelogh 1698, Tredeler 1857) and is W tref 'farmstead, homestead' + the personal-name Telerch, lenited initially in the place-name after a feminine noun, 'Telerch's farmstead'. The personal-name is itself compounded of the Welsh honorific prefix ty- + a masculine personal-name Elerch, which can also be found on its own as the name of a village in Cardiganshire, earlier Eleirch in all probability as it is that form which is used by Dafydd ap Gwilym in another of his poems.19 It is the failure fully to comprehend this point which has led to the mistaken belief that