We find in Irish genealogies occasional names of the Túatha Dé Danann. We might explain these facts simply as arising out of the euhemeristic tendencies of the Irish genealogists, according to which the Christian historians endeavoured to change the old Irish nature gods into old kings; but such a tendency must have been supported somehow by the old tradition, for instance by the occurrence of the Túatha Dé Danann in the old pedigrees, or by a tradition according to which the old gods lived on the earth. Such traditions are by no means rare in the mythical history of nations. And, further, we must not forget that there were different strata of population in ancient Ireland, as e.g. Fir Bolg, Ulstermen, Picts and Milesians, and so it would be most natural to regard the Túatha Dé Danann as such a tribe, especially since some races derived their origin from them.
The name Túatha Dé Danann probably belonged only to some of these síde, and was extended by the Lebor Gabála to all such beings. It was the same case as with the Fir Bolg: the territory of Bolg is proved by L.U. 56 /T.B.C. l. 87 to have been somewhere near Roscommon, as L.L. 56a has instead of Bolga: Badbgna. This Bolga (acc. plur.) was thus a name of local character, and Lebor Gabála has changed it to the name of a whole race. Now the cycle in which Túatha Dé Danann play a really important rôle is the cycle represented by Cath Maighe Tuireadh and similar stories, and even this Cath Maighe Tuiread is localised in Connaught, and the memory of this battle survives there to our own day. (I have heard it as cath na bpunnann) Take now the Ulster saga. What have the Túatha Dé Danann to do there? There were obviously no traditions of such a character. Here the supernatural characters appear only as síde. The same holds true for the Érnai cycle (Conaire Mór). Here the síde have a prominent role, and their supernatural character is here quite clear, but there is no sign that there
