To discuss this question properly we must consider the butterflies of each geological horizon separately.
The nearest living ally ofNeorinopis sepultais, with little doubt,Neorina Lowi, which, like the other members of the genus, is found in the Indo-Malayan region. The same is strictly true of the species of Zophoessa, Debis and Lethe, with which we have been obliged to compare this fossil. Cœlites has also been used in comparison, and most of the species of this group belong to the same region, although one is described by Felder from Celebes on the confines of the Austro-Malayan region. We have also pointed out (as Butler has done, but in incorrect points) its relation to Antirrhæa, a Brazilian genus, but this is too distant to be given much weight. The closest allies ofN. sepultaare to be found in the Indo-Malayan region.
The same is true, but not to so striking a degree, ofLethites Reynesii. We have compared this also to Debis, Lethe and Neorina, and especially to the two former; and all three of these genera, which are certainly its nearest allies,are strictly confined to the Indo-Malayan region. It is, however, also related, but in a secondary degree, to Enodia, Cercyonis and Maniola, which are genera appertaining to the north temperate zone of both hemispheres.
Coliates Proserpinafinds its nearest living representatives in the genus Delias, which also is strictly confined to the Indo-Malayan region. Thyca and Prioneris are closely related, the latter of which is limited to the same district and the former to the Indo-Malayan and Austro-Malayan regions.
Thaites Ruminianais represented in recent times by the genus Thais, which is confined to the Mediterranean district, within which Aix lies. An allied genus, Archon, is also restricted to the same region. Sericinus, however, and Eurycus, with which we have been obliged to compare it in many points, are found only in the East, the former in China, the latter in Australia; while on the other hand, Parnassius, a genus it quite as much resembles, is limited to alpine and subarctic regions of the northern hemisphere.
The relations ofPamphilites abditaare very different. I have searched carefully for very closely allied forms among East Indian Urbicolæ; but, while it doubtless is not far removed from some of them, its more intimate relationships are certainly with insects from tropical America and especially with Pansydia and Carystus.
Three out of the five Aix butterflies, therefore, find their nearest living allies in the Indo-Malayan region, one is most closely related to forms now found in tropical America and one is at home in its own resting place.
Thanatites vetulais the only butterfly yet found from this horizon, and this is closely related to Thanaos, a genus belonging to the north temperate zones of both hemispheres, but vastly more developed in the new world, which has at least four times as many species as the old, some of them extending into the subtropical regions. The genera adjacent to Thanaos are purely American, although tropical or subtropical, and therefore the Aquitanian butterfly looks toward subtropical North America for its relatives of the present day.
Only a single one of these butterflies,Mylothrites Pluto, belongs to an extinct genus. Its nearest living representatives are to be looked for in the genera Mylothris and Hebomoia, the former of which finds its highest development in torrid Africa, while the latter is confined to the Indo-Malayan and Austro-Malayan regions.
The other two belong to modern genera, Eugonia (E. atava) and Pontia (P. Freyeri). These two genera are very similar in their distribution, spreading, like Thanaos, above referred to, over the north temperate regions of both hemispheres. Eugonia, however, is represented equally in Europe and America, while Pontia is considerably richer in species in the Old World than in the New; yet when we look into the distribution of the neighboring genera we shall find a result somewhat similar to the case of Thanaos. Taking into consideration, in the one case, the present distribution of the genera Hypanartia, Polygonia, Papilio and Hamadryas,[AQ]and on the other of Neophasia, Tatocheila and Leptophobia, we shall find that the largest development of these groups of genera has been in the New World rather than in the Old, but in those parts of the New World which lie on the tropical confines of the temperate zone.
Two of the more recent species of fossil butterflies are therefore at home where they are found, although the present development of the group of genera to which they belong finds its fullest expression in America; while the third species follows most of those from the lower tertiaries in seeking its allies of to-day in the tropics of the old world.
Undoubtedly the material at our disposal is, as we have already remarked, far too meagre to present any generalities of importance, so long as they are unsupported by external proof. This aid we can claim in considering the facts we have presented concerning the present distribution of the genera of butterflies most nearly allied to those once living in the neighborhood of Aix. The careful researchesof Count Saporta upon the rich flora of this region at the same epoch, points to very nearly the same results as are here indicated. In hisExamen des flores tertiaires de Provence,[AR]when writing of the characteristics of the Aix flora, Count Saporta says (page 150) that about one-fifth of the families represented in it are now strangers to Europe; that fifty-one genera have an exotic and more or less tropical aspect, and that forty out of seventy-four, or about one-half, if not exclusively tropical, inhabit the warmer parts of southern regions, or, in small numbers, temperate extra-European countries. The result is still more striking, if species are considered, of which there are at least eighty whose individual analogy with living species is sufficiently clear to yield results of great probability. “De ces espèces,” to use his own words, “12 seulement correspondent à des espèces de l’Europe moyenne, 6 à des espèces de l’Europe méridionale, 18 en tout. Les espèces correspondant à des formes de l’Amérique septentrionale ou des régions élevées de l’Amérique tropicale, sont au nombre de 10; celles qui répondent à des formes de l’Amérique tropicale s’élèvent à 9 …; 3 correspondent à des espèces du Cap et 2 à des espèces des îles Atlantiques et de la Barbarie; 14 représentent des formes particulières aux Indes ou aux îles de l’Archipel indien et 30, enfin, correspondent à des formes australiennes. Le groupe australien est donc le plus considérable, si on les prend isolement. En les réunnissant, on voit que sur les 80 et quelques espèces, 28 à 30 seulement correspondent à des formes habitant aujourd’hui l’Europe et l’Amérique du Nord, en y comprenant même les parties méridionales de ces continents; tandis que 57 au moins, soit 60 en nombre rond, représentent des formes tropicales ou subtropicales, et dans ce nombre 40 au moins, c’est-a-dire la moitié du nombre total se rapportent au Cap, aux [151] Indes orientales où à l’Australie; de sorte que le caractère dominant de cette flore est encore Austro-indien, quoique dans une proportion déjà décroissante par rapport à l’âge précédant.”
This was published in 1861, and would accord entirely with what we know of the butterflies of Aix and their nearest allies. But eleven years later, after studying the great amount of material which had meanwhile accumulated, Saporta seemsto have reached different conclusions, for in hisRevision de la Flore des Gypses d’Aixhe states that the affinities of the eocene vegetation of Aix are with southeastern Asia and with Africa, and lists of analogous species are given, showing that twenty-two Aix species are to be compared with similar types in Asia, and forty with those of Africa. So that African forms much surpass the Asiatic in the eocene flora of Aix. This is particularly true, he says, with reference to the region of Africa between Abyssinia and the Cape of Good Hope. “C’est là évidemment le pays qui nous offre le tableau le plus ressemblant de ce que devait être le midi de la France, et c’est aussi vers ce même pays, ne l’oublions pas, que nous avons été ramenés par l’examen des autres élémens de la flore, spécialement par la proportion relative des deux grandes classes et des familles prédominantes.”[AS]The African element seems to be almost altogether wanting in the eocene butterflies, while the Asiatic predominates. In a chart accompanying Count Saporta’s paper, however, he represents the present limits of theprincipal generanoticed in the flora of the gypsum of Aix by means of colored lines. These lines cluster remarkably along the southern borders of Asia and extend over a large part of Africa and across the ocean to America, and particularly toward the southern United States and the Antilles. Based on the distribution of these principal genera alone, the flora of the southern border of Asia would show a closer affinity to that of eocene Aix than would that of any equivalent belt in Africa; and if we may suppose that our relics of butterflies represent the principal genera then existing, we should trace a somewhat similar chart, but for the entire absence of African types; for subtropical American types mingle with those of the Mediterranean district and especially with those of the Indo-Malayan region. Count Saporta shows in his memoir just quoted, as before, that the relations of the eocene flora of Aix to that of the present Mediterranean basin were more restricted than its relations to exotic types, but in a letter to me he writes: “Ces affinités [les affinités présumées de la flore d’Aix] sont d’une part avec la région Méditerranéen, de l’autre avec l’Afrique et les Indes orientales. Les affinités miocènes avec l’Amérique sont postérieures.” These later American affinities are, however, foreshadowed among the plants and also, as wehave seen, in the Pamphilites of eocene Aix. They appear again, and very decidedly, when we reach the miocene itself, for the affinities of the butterfly from Rott, and two of the later butterflies from Radoboj (where first we meet with truly modern types), are certainly with America in the first instance, and secondarily with the whole north temperate zone. While the last of the Radoboj butterflies shows still the remains of the earlier affinities of the Aix flora in finding its nearer existing types in Africa and southeastern Asia. The results we reach in considering the Aix butterflies are not, however, in accordance with those drawn from the insects of the same locality by Professor Heer. He writes:[AT]—
“A Radoboj, … on rencontre une plus forte proportion de formes tropicales [than at Œningen].…Cette faune des insectes s’harmonise parfaitement avec le flore de Radoboj qui, ainsi que nous l’avons prouvé précédemment, a un caractère plus méridional que celle d’Œningen; ce qui s’expliquerait par sa plus grande ancienneté.Comme il résulte des recherches de M. G. de Saporta qu’Aix appartient à l’étage ligurien, on devrait s’attendre à y rencontrer encore plus de formes tropicales qu’à Radoboj. C’est tout le contraire, si bien qu’en m’appuyant sur la faune et en voyant que Aix avait 10 espèces en commun avec Radoboj et 4 avec Œningen, j’avais rapporté précédemment les terrains d’Aix à la même époque que ceux de Radobo; et je les avais rangés dans le Mayencien. Quatre genres ont disparu.… Tous les autres genres vivent encore dans la Provence, mais ce sont, comme à Œningen, presque tous des genres qui occupent une aire géographique très vaste.… On ne peut pas dire que la faune des insectes d’Aix contredise positivement l’idée que cette localité avait un climat sous-tropical, cas presque tous les genres que l’on y a observés jusqu’à présent s’étendent jusque dans la zône sous-tropicale, néanmoins cette faune ne fournit que bien peu de preuves positives, tandis que, comme M. de Saporta l’a démontré, la flore est riche en formes méridionales.”
“A Radoboj, … on rencontre une plus forte proportion de formes tropicales [than at Œningen].…
Cette faune des insectes s’harmonise parfaitement avec le flore de Radoboj qui, ainsi que nous l’avons prouvé précédemment, a un caractère plus méridional que celle d’Œningen; ce qui s’expliquerait par sa plus grande ancienneté.
Comme il résulte des recherches de M. G. de Saporta qu’Aix appartient à l’étage ligurien, on devrait s’attendre à y rencontrer encore plus de formes tropicales qu’à Radoboj. C’est tout le contraire, si bien qu’en m’appuyant sur la faune et en voyant que Aix avait 10 espèces en commun avec Radoboj et 4 avec Œningen, j’avais rapporté précédemment les terrains d’Aix à la même époque que ceux de Radobo; et je les avais rangés dans le Mayencien. Quatre genres ont disparu.… Tous les autres genres vivent encore dans la Provence, mais ce sont, comme à Œningen, presque tous des genres qui occupent une aire géographique très vaste.… On ne peut pas dire que la faune des insectes d’Aix contredise positivement l’idée que cette localité avait un climat sous-tropical, cas presque tous les genres que l’on y a observés jusqu’à présent s’étendent jusque dans la zône sous-tropicale, néanmoins cette faune ne fournit que bien peu de preuves positives, tandis que, comme M. de Saporta l’a démontré, la flore est riche en formes méridionales.”
It should be remarked, however, that the insect fauna of Aix is as yet little known; that these observations of the learned Zurich Professor were founded upona material exceedingly meagre, in comparison with the present vast accumulations of the museums of Marseilles, Paris and Aix; we may hope soon to become familiar with them through the careful researches of M. Oustalet; and these will show that the beds of Aix are, perhaps, even richer in fossil insects than those of Œningen.
The American affinities of the Rott butterfly are in entire harmony with what is known of the other insects of the lignites of the Rhine, where, says Professor Heer:[AU]—“On retrouve également des types américains, qui appertiennent à l’Amérique tropicale et sous-tropicale.”
As to the flora of Radoboj, Professor Heer writes in the work just quoted (p. 96): “Les plantes de la zône tempérée sont représentées plus fortement qu’à Sotzka,” and of the latter place he says (p. 95), after speaking of types of the temperate zone: “Cependant ces espèces se trouvent fort à l’arrière-plan en comparison des formes tropicales et subtropicales, parmi lesquelles prédominent … les formes indo-australiens; néanmoins les formes américains, loin d’y faire défaut, sont représentées par des types assez nombreux et nettement accusés.” As a whole, therefore, the affinities of the tertiary butterflies seem to be precisely what we should have anticipated from a study of the vegetation of the period.
We close this portion of our subject with a tabular view of the results we have reached in considering the affinities of the tertiary butterflies with living types, in which the countries, where the living allies of the fossil forms are now found, are placed in the right-hand columns according to the degree of affinity of their inhabitants to the tertiary species against which they are placed.
Nine well authenticated fossil butterflies are now known, all from the European Tertiaries; five of these have been found in the gypsum beds of Aix in Provence, southern France, belonging to the Ligurian, a division of the upper eocene; one in the lignites of Rott in the Rhenish Provinces of Prussia, belonging to the Aquitanian, or lower miocene; and three in the marls of Radoboj in Croatia, Austria, appertaining to the Mayencian or middle miocene. Our present knowledge, then, places the apparition of butterflies towards the end of the lower tertiaries.
As a general rule the specimens thus far discovered are in a fair state of preservation, and especially are those parts preserved which enable us, with considerable confidence, to determine their exact affinities. Three of these insects belong to the highest family of butterflies, Nymphales, four to the Papilionidæ, and two only to the Urbicolæ. If it be considered probable that the lowest of these families was the oldest, we can reasonably account for the scarcity of its members in the tertiary strata by the fact that their almost universally robust and muscular frame enables them to maintain flight when they have lost all but the merest stubs of wings. They would thus seldom meet their end by falling into pools of water, or if at last they did, it would be with fragments of wings whose affinities could not be traced. This supposition would be strengthened on noticing that one of the two fossil forms classed here,Thanatites vetula, belongs to a group of genera which comprises the very feeblest flyers in the family; and by the further consideration that two of the three fossil Nymphalids belong to the weak-winged Oreades. Eugonia, as well as Pamphilites, were doubtless strong and bold flyers; while the genera of Papilionidæ were moderately endowed. To proceed further in the analysis of their structural relations, two of the three Nymphales belong, as we have said, to the highest group of butterflies, the Oreades, represented now by the dark brown butterflies of our meadows; the remaining one to the Præfecti, a group of gaily attired butterflies with angulated wings like our common thistle butterfly, the cosmopolite. Of the four Papilionidæ, three belong to the Danai; two of these three to the group Fugacia, represented by our common yellow brimstone butterflies; the third to the Voracia, or white butterflies of the garden, so destructive to cabbages and other cruciferous plants. The fourth Papilionid belongs to the lower subfamily Papilionides; not, however, to that group which contains our swallow-tailed butterflies, but rather to an allied tribe, represented in America only by the Parnasii of the Rocky Mountain region. The two Urbicolæ are divided between the Hesperides and Astyci, the former closely related to the dingy, sylvan hesperians of early spring, seldom seen but by the naturalist; the latter to the tawny, brisk little skippers busy around the flowers in June.
But a single family of butterflies, then, is unknown in a fossil state,—that ofRurales; and since this comprises, in the main, insects of exceedingly delicate structure and of small size, their absence is by no means unaccountable. Yet, as we shall see further on, there are intimations of the presence of some of their caterpillars in amber, and an obscure and doubtful reference to a fossil Polyommatus from the beds of Aix.
If we enquire where the allies of these nine fossil butterflies are now living, we must seek for those of four of them in the East Indies; for those of three of them in America, and especially in that part lying on the confines of the tropical and north temperate zones; for those of one of them in the north temperate zone of both Europe-Asia and America; and for those of one in the Mediterranean district; for those of two only, therefore, out of the nine, or less than one-fourth, in the region where the fossils were discovered. Analyzing this point still further, we notice that three out of the four species whose living allies are to be sought in the East Indies come from the older deposits of Aix, and that only one of the two remaining Aix species shows special affinities to American types; we thus find here, as among other insects and among the plants, a growing likeness to American types as we pass upward through the European tertiaries.
The study of the floras of the European tertiaries has proceeded so far that in most cases we are able to find, in the very beds where the butterflies occur, plants which we may reasonably judge to have formed the food of these insects in their earlier stages. In but a single instance is the family of plants, upon which it was necessary, or almost necessary, to suppose the caterpillar fed, entirely absent from tertiary strata; and since this family is the Cruciferæ, which in its very nature could scarcely have left a recognizable trace of its presence, the exception has no force.
After presenting these facts, for convenience sake, in a tabular form, we will pass on to the enumeration of those fossils which have been referred to butterflies, but whose exact position is still unsettled.
In the earliest accounts that we have found, including all those in the last century, the generic term Papilio was used for all Lepidoptera, and therefore we cannot be certain whether butterflies or moths are meant. Hueber’s plates, even, are so inferior that they afford no additional aid; but those of Sendel possibly represent, as we have noticed in the Bibliography at the commencement of this memoir, the early stages of butterflies preserved in amber. The only other direct references to butterflies preserved in amber are the following: Gravenhorst,[AV]in his enumeration of amber insects, gives under the Lepidoptera forty specimens referable to Tineæ and Tortrices, and besides these “mehre Raupen, sämmtlich, wie es scheint, Schildraupen, denen des Papilio W. album ähnlich.” The probable nature of the ancient forest yielding amber renders it unlikely that any butterflies in their perfect state would be found in it. As a rule, butterflies are eminently fond of the light. This has already been remarked by Menge:[AW]—“Das fehlen gröszerer Schmetterlinge im bernstein deutet auf einen finstern undurchdringlichen urwald, den die kinder des lichts gemieden haben.” Yet as some Theclas do feed upon coniferous trees, it is not impossible that the onisciform larvæ, referred to by Gravenhorst, may belong to this group. As far as we can discover, no further reference is made to them, excepting by Giebel and Bronn in some of their lists and enumerations of fossil insects. The writings of Berendt, Menge and others, all bear testimony to the great rarity of Lepidoptera in amber, and most of those which have been discovered belong to the lowest two families, above referred to.
Dr. Hagen informs me that he has himself seen specimens of large butterflies in amber, but that these proved to be falsifications, recent European insects likePieris rapæ, etc., having been enclosed between slabs of amber, which were then fastened together and the edges roughened, all in so clever a manner that one would not suspect them to be spurious. These specimens were manufactured many years ago, and it is not impossible that it is to one of them that Hope refers in 1836, as found in the collection of Mr. Strong, though why he should quote Berendt as authority I cannot discover.
Heer, in the introduction to the lepidopterous portion of his “Insektenfaunader Tertiärgebilde von Œningen,” says (p. 175): “Karg erwähnt zwar eines sehr schönen Œninger-Schmetterlings, der nach Zürich gekommen sein soll. Allein hier findet sich dieser nicht und die Angabe verliert noch mehr an Werth, wenn wir berücksichtigen, dass Karg das Thier nicht selbst gesehen hat.” Karg’s memoir in the “Denkschriften der Schwäbischen Gesellschaft der Aerzte und Naturforscher,” T. I., I have been unable to examine.
Boisduval, in his final report uponNeorinopis sepulta, remarks that Count Saporta had written him that many years previously he had sent to the Paris Museum a “Polyommate fossile” from Aix. Count G. de Saporta, in reply to my inquiries concerning this specimen, says that his father can give me no further information concerning this specimen; nor could M. Oustalet and myself, in our search through the fossil insects of the Jardin des Plantes, discover any such relic.
In a recent number of “Nature” (No. 266), Mr. E. J. A’Court Smith writes of the discovery at Gurnet Bay in the Isle of Wight, of an insect bed in which were found, among other things, “a variety of flies, butterflies, and one or two grasshoppers;” no further information has yet been published concerning these relics, and my inquiries upon the subject have not, as yet, elicited any definite response.
Fig. 2.Cyllonium Boisduvalianum Westw.
Fig. 2.
Cyllonium Boisduvalianum Westw.
These two insects were figured by Westwood in the Quarterly Journal of the Geological Society of London for November, 1854, the former (reproduced in our fig. 2) on Pl. XVII, fig. 17; the latter (reproduced in our fig. 3) on Pl. XVIII, fig. 27. Of the former he makes the following remarks:[AX]“Pl. XVII, fig. 17 represents a number of fragments of delicate tegument, covered with minute puncturesand traversed by straight and somewhat radiating veins, which appear like portions of the hind wing of some species of Butterfly, entirely denuded of scales.” The name is given to it in a note to the explanation of the plates, p. 395. Concerning the second he says:[AY]“Pl. XVIII, figs. 27 and 30, appear to be portions of the hind wings of some species of Butterfly; still they have very much of a vegetable aspect. The surface is covered with minute punctures, which may be the cells for the insertion of the quills of the coloured scales, which are all removed, supposing the specimens to be Lepidopterous.” The name we have quoted is given only to fig. 27, in a foot note on p. 396.
Fig. 3.Cyllonium Hewitsonianum Westw.
Fig. 3.
Cyllonium Hewitsonianum Westw.
I have not been able to find, even with Mr. Brodie’s help, the first specimen referred to; but an examination of the original of the latter (see fig. 3) proved that, while it is unquestionably an insect, it cannot be referred to the Lepidoptera; the punctures referred to are both too large and much too irregularly disposed to have been the points of insertion of the scales; they are probably the marks of the insertion of hairs, such as are not uncommonly seen irregularly scattered over the wings of insects belonging to the other suborders. As the figure of the first species closely resembles in this particular the one I have seen, I am forced to the conclusion that neither of these wings are lepidopterous. Plainly, the only reason why a new generic name was appended to these forms was that their remains were too fragmentary to afford the slightest guess as to what modern genus they might be referred. The fossils came from the English Purbecks.
The first notice I find of this remarkable and very interesting fossil is that published in various literary and scientific London journals reporting remarksgiven at a meeting of the Entomological Society of London, and which afterward appeared as follows in their Proceedings:[AZ]
“Mr. Butler exhibited a remarkably perfect impression of the wing of a fossil butterfly in the Stonesfield slate. It appeared to be most nearly allied to the now existing South American genus Caligo.”
Fig. 4.Palæontina oolitica Butl. The neuration, after Butler’s first sketch.
Fig. 4.
Palæontina oolitica Butl. The neuration, after Butler’s first sketch.
A full description of this insect soon appeared in the author’s “Lepidoptera Exotica,” accompanied by a plate; both were afterward republished in the “Geological Magazine.” In fig. 4 we reproduce fig. 1 of his plates, representing the neuration of Palæontina; and in fig. 5, fig. 2 of his plates, subsequently copied by “The Graphic.” A description of the genus and species is first given, which it is unnecessary to reproduce here; afterward, the following remarks:
“[126] Though a British insect, this species belongs to a group so completely tropical that I do not hesitate to describe and figure it in the present work; its nearest allies are the genera Caligo, Dasyophthalma and Brassolis, all three essentially tropical American genera.
Fig. 5.Palæontina oolitica Butl. Facsimile of Butler’s first sketch.
Fig. 5.
Palæontina oolitica Butl. Facsimile of Butler’s first sketch.
“P. ooliticais especially interesting, as being the oldest fossil butterfly yet discovered;the most ancient previously known to science having been found in the Cretaceous series (white sandstone of Aix-la-Chapelle[BA]), whilst the bulk of the known species are from the Lower Miocene beds of Croatia; it is also interesting as belonging to the highest family of butterflies, and to a subfamily intermediate in [127] character between two others, namely, the Satyrinæ and Nymphalinæ, whilst the more recently discovered fossils are referable, with one exception, to the two latter groups. The nervures appear to have been impregnated with iron, which will partly account for their well-defined condition.”
Happening to be in London not long after the publication of the description and illustration of this insect, I took pains to make a very careful examination both of the original specimen, which Mr. Charlesworth kindly allowed me to study at my leisure, and of its reverse, which is preserved in the School of Mines, Jermyn street. I mentioned to Mr. Butler and to others, my conviction that the insect was to be considered homopterous rather than lepidopterous, and on my return to America, exhibited before the Natural History Society of Boston, drawings which I had made from the originals; my comments at that time were published very briefly, as I was reserving the proof of my statements for the present paper. Mr. Butler, however, was induced by this publication[BB]to examine the reverse at the Jermyn street Museum, and although he had been supplied by me with a rough tracing of the drawing I had taken of it, he failed to be convinced of any mistake, and published a paper in defence of his own view in the Geological Magazine for October, 1874. In this paper he gives new drawings of the insect, quotes portions of letters in which I had expressed my opinions upon the nature of the fossil, gives the remarks referred to from the “Proceedings of the Boston Society of Natural History,” and makes, among others, the following comments.
Fig. 6.Palæontina oolitica Butl. Facsimile of Butler’s second sketch.
Fig. 6.
Palæontina oolitica Butl. Facsimile of Butler’s second sketch.
“Seeing that Mr. Scudder had made his views public, I felt that it was time for me to take similar steps on my side. I therefore availed myself of an early opportunity of again visiting Jermyn street, where, through the courtesy of the officers, I was enabled to make a sketch of the impression in the Museum. Ifound it impossible to make a tracing of it, and therefore drew the whole by measurement. This sketch is now produced on Pl. XIX, fig. 4 [see fig. 6]; and any body can judge for himself whether or not it is more perfect than that which I previously figured (see Geol. Mag., 1873, Vol. X, p. 2, Pl. I, fig. 2 [see fig. 5]).”
“In order to show the extent to which the Jermyn street example is deficient, I have restored it (fig. 5 [our fig. 7]), filling in the blanks from Mr. Charlesworth’s specimens. By comparing the latter with the wing ofDasyophthalma(fig. 1), andCicada(fig. 2), one may come to a pretty accurate conclusion as to the group of insects to which it ought to be referred.”[BC]
The neuration of Lepidoptera as a group is the simplest in the whole order of insects, if we except that of the elytra of Coleoptera; this is due, doubtless, to the fact that their wings are heavily scaled, concealing the nervures; just as in Coleoptera, the thickness and opacity of the fore wings often completely masks the neuration.
Fig. 7.Palæontina oolitica Butl. The neuration, after Butler’s second sketch.
Fig. 7.
Palæontina oolitica Butl. The neuration, after Butler’s second sketch.
The normal number of veins in the wings of insects is six, disposed to a certain extent in pairs; the middle pair usually ramify to a greater extent than the others, and support most of the membrane of the wing. In butterflies the foremost vein is always absent and very commonly the hindmost, so that there are but five (often but four) principal veins, usually designated, though not very appropriately: costal, subcostal, median, submedian and (when present) internal, reciting them in their order from in front backward. The costal, submedian and internal nervures are invariably simple and terminate at the margin, or are occasionally lost in the membrane of the wing. The subcostal and median nervures, on the other hand, are as invariably forked,and with their branches support nearly the entire wing; the subcostal nervure curves downward and the median upward so as to meet, or nearly to meet, not far from the middle of the wing, and to enclose between them a large space called the discoidal cell; the branches of the median nervure are all thrown off from its lower edge before union with the subcostal; the principal branches of the subcostal nervure are, on their side, thrown off from its upper edge; but, as the nervure curves downward at the extremity of the cell, another set is thrown off (at least in the fore wings) from the lower edge; and it is these veins, rather than the subcostal nervure proper, which unite with the median to close the cell.[BD]None of the median, nor any of the inferior subcostal nervules are ever branched; but at the apex of the wing, where the play of neuration is usually the greatest, the last superior subcostal nervule is occasionally forked in the front wing. This is the only forked branchlet in either of the wings.
The last figure ofP. ooliticagiven by Mr. Butler agrees in all its essential features with his first illustration. They both represent a front wing with four principal nervures,—costal, subcostal, median and submedian; the costal nervure is swollen at the base and extends, unbranched, to the tip of the wing; the median nervure is three-branched, the three forks simple, equidistant, emitted from the apical half of the vein, which at its extremity is united by a cross vein to a branch of the subcostal, closing the cell; the submedian nervure is simple and divides the space between the median vein and the margin of the wing. So far all is in accordance with the lepidopterous type; but when we examine the subcostal vein, which occupies nearly half the wing, the resemblance ceases altogether. This vein is represented as bearing no superior branches, but as sending out from itsinferiorsurface three distinct veinlets, the first and second of which again emit a tributary from their inferior surfaces. This is a structural anomaly which finds no counterpart whatsoever in any family of butterflies. So that should we accept Mr. Butler’s own sketch of the fossil as correct, it would be impossible to consider the wing that of a butterfly.
In his description of the insect Mr. Butler compares the neuration to that of Caligo, and says its nearest allies are Caligo, Dasyophthalma and Brassolis. In his latter paper he figures the wing of a Dasyophthalma by way of comparison. In the genera named all the branches of the subcostal nervure are simple, and are thrown off from the superior surface, excepting the single set which is emitted from beneath, and which marks (as in all butterflies) the limit of the discoidal cell; this corresponds fairly with the first set of inferior veins emitted by the subcostal vein in the fossil; for the other sets, however, no counterpart will be found in the living types.
Fig. 8.Palæontina oolitica Butl. Corrected sketch of the neuration.
Fig. 8.
Palæontina oolitica Butl. Corrected sketch of the neuration.
It was probably Mr. Butler’s want of familiarity with fossils that led him to overlook several features which can be seen in these originals. Having first traced the outline of the wing and the general course of the veins directly from the specimens, I subsequently filled in by measurement all the other parts which I could follow, studying each vein, or supposed vein, with the utmost care, from one end to the other of its course. The result of that study is presented in fig. 8, which differs essentially in its details from the illustrations given by Butler, and looks, as he himself confesses, “exceedingly anti-lepidopterous.” In the first place, the wing is much narrower than depicted by him; and at the extremity of a vein (the submedian vein of Butler’s sketch) there is a slight but decided bending inward of the membrane, as very frequently occurs at the line of demarcation between the middle and inner area of the wing in all or nearly all the lower suborders of insects, but never, so far as I am aware, in Lepidoptera. What he has given as a simple costal vein is neither swollen at the base nor simple, but has two inferior branches near the middle of the wing, united near their origin by an oblique cross vein. Branching of the costal vein is unknown in Lepidoptera; but if it should be claimed that this might be the subcostal, just as much difficulty will be encountered with the structure and relationship of the veinlets below, which must then be considered as belongingto the median vein; in no Lepidoptera can any such irregularity be shown, nor so disproportionate a magnitude of the area covered by the median nervure and its branches; a branched internal vein and cross-veins, which probably united all the longitudinal nervures at no great distance from the outer border (but which can only be certainly predicated for the lower three median interspaces), place this insect wholly beyond the pale of the Lepidoptera. It is but fair to say that Mr. Butler, having examined the original after he had in his possession a tracing of fig. 8, denies the existence of the cross-veins; there is one point, however, which an unprejudiced examination of the fossil cannot fail to show; that Butler’s “fourth branch” of the subcostal[BE]arises not from his third branch, but from his upper discoidal vein; if he can reconcile either this or the points already referred to (on the supposition that his sketch is otherwise an accurate one) with the neuration of any group of butterflies, the writer will be the first to acknowledge it.
As our only purpose in this place is to deny the lepidopterous character of Palæontina, it is unnecessary to say anything in defence of the view we have expressed of its homopterous affinities; the superior position of the cell, the position and character of the lower cross veins (which we believe really traversed the entire wing), with their origin at the indentation of the lower border, suggest such a relationship, although there are not a few points in which it differs somewhat strikingly from living types.
The discovery of a fossil in the cabinet of the Rev. Mr. Brodie, which was found in England at the same or nearly the same horizon, asP. oolitica, and which seems to be a pupa case of one of the Cicadida of rather unusual size, renders my suggestion more worthy of credence.
At the conclusion of his latter paper Mr. Butler draws attention to the fact that Messrs. Westwood and Bates had expressed their agreement with his views. It should, however, be borne in mind, that, so far as appears from any facts which have been published, these gentlemen, whose well considered views upon the subject would unquestionably be of great weight, expressed this assent only upon a brief evening examination of a very obscure fossil in a poorly lighted hall, and before any one had questioned its lepidopterous character.