Of the five butterflies from Aix, two belong to the Oreades (Neorinopis sepulta and Lethites Reynesii) the food of whose caterpillars at the present epoch has invariably been found to be either GramineÆ or, occasionally, CyperaceÆ. Both of these groups are present in the deposits of Aix, the former being represented by ten species of Poacites, and the latter by a Cyperites;[AG] and it is in the highest degree probable that these formed the sustenance of the Oreades of that epoch. A third species (Pamphilites abdita) belongs to the Astyci, a group whose principal food is the same family of plants, GramineÆ, although some species have been found also upon Althea, Malva and Lavatera (MalvaceÆ), Trifolium, Coronilla and ?Lespedeza (LeguminosÆ), Plantago (PlantaginaceÆ), and Maranta (ScitamineÆ). Of these families the LeguminosÆ only are found at Aix, and in abundance, even including a plant doubtfully referred to Trifolium. It is, however, far more probable that Pamphilites lived upon grasses; and it is not a little strange that the GramineÆ, the probable food-plants of three of the five butterflies known from that fauna, were among the rarest of the plants; that is, their proportion to the whole phanerogamic flora was about the same as now obtains in New Guinea or New Grenada, countries the least favored in this respect.[AH] The proportion of the GramineÆ and CyperaceÆ to the whole of the Phanerogamia in Europe of to-day is, probably, about the same as in the United States (more than seventeen per cent.) and much greater than in the East Indies. The limited number of known fossil butterflies does not give great weight to any general considerations based upon them, but it may at least be worth while to remark that Aix, in Eocene times, had, in the point referred to, an assemblage of plants much better comparable with the East Indian flora of the present day than with the modern European flora, the proportion of known GramineÆ, etc., to the Phanerogamia being five per cent., while the proportion of its grass-feeding butterflies to the other rhopalocerous Lepidoptera is sixty per cent. To judge simply by the catalogue of the East India Museum, the only authority upon East Indian butterflies extant, the present proportion of gramnivorous to non-gramnivorous butterflies is as 1: 5·2, while in Europe it is as 1: 3. Eocene Aix, then, had a European proportion of Satyrids, composed, as will be seen, of species of an Indian aspect, feeding upon plants essentially temperate, but, as in tropical countries, numerically unimportant.

The Danai, to which the fourth species from Aix (Coliates Proserpina) belongs, feed almost exclusively upon LeguminosÆ, and these have recently been found in great abundance at Aix. Count de Saporta enumerates one species each of ?Trifolium, Caragana, Ervites, Sophora, Micropodium, Cercis and Gleditschia, two of Phaseolites and six of CÆsalpinites, belonging to the PapilionaceÆ, besides nine Acacias and a Mimosa of the MimoseÆ, and four species of uncertain relations; making a series larger than he has found in any other family.[AI]

Of these, two species of Phaseolites, one of Sophora, eight of Acacia and two of Leguminosites are specified as coming from the lower beds, where Coliates itself is found. But Coliates is most closely allied, as we have said, to a group of Indian forms, and the food plants of their caterpillars is almost wholly unknown. A species of Delias, however, to which genus Coliates has been specially compared, is stated to feed, not upon a leguminous plant, but upon Dioscorea, one of the Yam family; and the presence in Aix of a species of a closely allied group, Smilax rotundiloba Sap., is announced by Count de Saporta. It is not improbable, therefore, that Smilax rotundiloba was the food-plant of the larva of Coliates Proserpina.[AJ]

The fifth Aix species is Thaites Ruminiana. It is most nearly allied to Thais of the present day, though it bears certain relations, as we have seen, to neighboring genera. Thais feeds principally at least upon Aristolochia[AK] and so, too, do Ornithoptera, Archon and some genera of swallow-tails; indeed, this seems to be a favorite food-plant with insects of this character. Parnassius, however, feeds on Sedum, Telephium, Sempervivum and Corydalis, especially on the first-named, one of the CrassulaceÆ; but nothing very closely allied to this is specified by Saporta from Aix; neither, also is Aristolochia, but it has been found not only in Radoboj[AL] in the Mayencian, but also, according to Heer, at Hohe Rhonen in Switzerland, which belongs to the Aquitanian, and has at least one plant (Laurus primigenia Ung.) in common with Aix. It seems, therefore, highly probable that either Aristolochia nervosa Heer, A. Aesculapi Heer, or a distinct species of the genus will yet be discovered at Aix,[AM] and may then be considered, as with little question, the food-plant of Thaites Ruminiana. If it be deemed hazardous to venture such an opinion, attention is called to the two following passages; the first is from the introduction to Heer’s paper on the fossil insects of Aix:[AN] “Dass indessen auch Weiden oder Pappeln [Populus] sich vorhanden, dÜrften der Bythoscopus muscarius und die Aphrophora spumifera [Homoptera] anzeigen, deren analoge lebende Arten besonders auf den BlÄttern und Zweigen dieser BÄume sich umhertreiben.” The second is a note in the errata to the translation of Heer’s work on the Climate and Vegetation of the Tertiaries[AO] by Gaudin: “Le Poacites 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.

The only butterfly found at Radoboj belonging to an extinct genus is Mylothrites Pluto, and this is a member of the same general group as Coliates, and feeds probably upon LeguminosÆ; for it is not so closely allied to Delias as Coliates is, but is more nearly related to Hebomoia, one of whose species, found in the East Indias, feeds upon Capparis.[AP] One species of Phaseolites, one of Sophora and four of Cassia, namely: C. hyberborea Ung., C. phaseolites Ung., C. lignitum Ung., and C. ambigua Ung., are recorded from Radoboj, and as Cassia is a favorite food plant among the larger species of Danai at the present day, we may fairly presume one of these CassiÆ to have afforded nourishment to Mylothrites Pluto. Moreover, no less than thirty-one species of LeguminosÆ in general, or between a ninth and a tenth of the whole known flora, are given by von Ettingshausen as occurring in Radoboj; so that in any case our Mylothrites must have found abundance of palatable food.

The food of Pontia Freyeri is doubtful. All the living species of the genus so far as known, feed upon CruciferÆ; within this family they do not seem to be at all particular, making use of a large number of genera, but in only a single instance are they known to attack the leaves of a genus (Reseda) belonging to an adjoining family. CruciferÆ, however, are excessively rare in the tertiaries of Europe, two species only being recorded, and this from the comparatively recent beds of Œningen. This is unquestionably due simply to the nature of the plants themselves, which scarcely could leave any trace of their existence; the almost complete absence of the herbaceous families of plants, even in the later tertiaries, is doubtless due to this fact. The plants nearest related to the CruciferÆ found near the horizon of Pontia Freyeri are a species of Nelumbium from GÜnzbourg in the Mayencian, and of Terminalia (T. radobojensis Ung.)—one of the CalyciflorÆ, from Radoboj itself. Perhaps in the absence of better evidence we may provisionally consider the latter to have been the food plant of P. Freyeri.

A single Radoboj species remains, Eugonia atava. The recent species of Eugonia feed particularly on Salix, Populus and Betula; also upon Ulmus, and occasionally on Ribes, and even on Hippophae. The first three seem however to be their proper food; and since the tertiaries of Radoboj contain fossils of all these genera, we need look no farther. There are specified: Salix apollinis Ung., sp., Populus latior Br., P. mutabilis Heer., P. Heliadum Ung., Betula Dryadum Brongn. and B. prisca Ett. Three species of Ulmus are also recorded from the same place.

Excepting in a single case, there is then no difficulty in finding, in the very hods in which the butterflies occur, remains of plants, which in all probability served them as food during the larval stage; and even in this single instance, a plant not far removed from those upon which species of the genus now feed, occurs in the same strata.