ciliatus Sap. n’est pas une glume de Graminée, mais plutôt une bractée ciliée de Peuplier.… Elle doit être probablement rapprochée d’une empreinte … provenant des mêmes couches et qui se rapporte également au genre Populus. Les organes voisins de ceux du Pop. Euphratica Oliv. dans la nature actuelle dénotent l’existence, à l’époque des gypses d’Aix, d’une espèce de Peuplier dont les feuilles sont encore inconnues, comme celles de l’Alnus cryptophylla Sap., mais que M. Heer avait indiqué d’avance, en se fondant sur l’observation d’un insecte fossile, le Bythoscopus muscarius! Nouvelle preuve du secours que peuvent se prêter en paléontologie les diverses branches de l’histoire naturelle.” The single species from Rott, _Thanatites vetula_, is closely allied to the modern Thanaos, whose species are numerous and feed upon a variety of plants, belonging to the families Cruciferæ, Leguminosæ, Umbelliferæ, Cupuliferæ, Betulaceæ and Salicaceæ. Most of the genera belonging to its tribe feed upon Leguminosæ, and these are the usual food plants of the species Thanaos also; whence it is probable that Thanatites had a similar taste. Now in the very beds of Rott, in which this butterfly was found, occur species of Betula, Salix and Populus, with numerous Querci and no less than eleven genera of Leguminosæ, mostly belonging to the Papilionaceæ; they are Templetonia (1 species), Robinia (2), Colutea (1), Phaseolites (2), Sphinctolobium (1), Dalbergia (1), Hæmatoxylon (2), Gleditschia (2), Cassia (3), Ceratonia (1), and Acacia (2). It is probably among these, and perhaps with greatest probability among the species of Hæmatoxylon and Gleditschia, that the food plant of Thanatites must be sought. Should leaves be found, in which a portion is bent over as if to form a nest, they should be submitted to the scrutiny of some one familiar with the larval habitations of _Thanaos Tages_; and should traces of silken fastenings be found in connection with them, or the marks of nibbling at the edges, the plant to which they belong may be considered with strong probability as the food of _Thanatites vetula_.