Hemming (1967) stated:-
Like Castnia [Illiger], 1807, discussed above, the nominal genus Castnia Fabricius was established in the erroneous belief that it was a genus of butterflies, whereas it is, in fact a genus of moths. By a Ruling given in Opinion 232 (1954, Opin. int. Comm. zool. Nom. 4 : 249-274), the name Castnia Fabricius was placed on the Official List of Generic Names in Zoology as Name No. 659.
Besides having been established as a genus of butterflies the genus Castnia Fabricius has an interest to specialists in the Rhopalocera, because the name of its type-species (Papilio icarus Cramer, ) is a homonym of the name of the type-species (Papilio icarus Rottemburg, 1775) of the Lycaenid genus Polyommatus Latreille, 1804. The fact that there was no available means for determining the relative priority of the specific names icarus Cramer and icarus Rottemburg was for long a source of embarrassment to specialists in the groups concerned. Similar difficulties existed also in the case of a considerable number of other pairs of names published in 1775 in the works not only of Cramer and von Rottemburg but also in those of Fabricius and others. In order that an end might be put to these uncertainties, this matter was submitted to the Commission which in its Opinion 516 (1958, Opin. int. Comm. zool. Nom. 19 : 1-44) gave directions under its Plenary Powers as to the relative precedence to be accorded to new names in these works published in the year 1775. Of the decisions so taken the one which is immediately relevant to the present case was that under which names published in Cramer's Uitl. Kapellen were given precedence below those in Rottemburg's celebrated paper in the serial Der Naturforscher. Thus, the name Papilio icarus Cramer, , the name of the type-species of Castnia Fabricius is invalid as a junior homonym of Papilio icarus Rottemburg, 1775. Following the adoption of the above Opinion, the Commission adopted a Direction (Direction 96, published in 1958 in Opin. int. Comm. zool. Nom. 19 : (i)-(xiv), in which it placed the objectively invalid name icarus Cramer , as published in the combination Papilio icarus, on the Official Index of Rejected and Invalid Specific Names in Zoology as Name No. 520. At the same time consideration was given (1958, loc. cit. 19 : (ix)) to the question of the oldest available name subjectively applicable to the type-species of Castnia Fabricius, this having become a practical question in view of the decision that the name Papilio icarus Cramer, objectively applicable to it had been ruled to be invalid. The conclusion then reached was that the oldest name subjectively applicable to this species was Castnia penelope Schaufuss, 1870 (Nunqu. otios. 1 : 9). Accordingly, in order to complete this case the Commission (loc. cit. 19 : (iii)-(iv)) placed the specific name penelope Schaufuss, 1870, as published in the combination Castnia penelope, on the Official List of Specific Names in Zoology as Name No. 1516.
Fletcher & Nye (1982) stated:-
P. icarus Cramer is a junior homonym of Papilio icarus Rottemburg, 1775, Naturforscher, Halle 6: 21; the priority of Rottemburg's work over that of Cramer was determined by the International Commission on Zoological Nomenclature, 1958, Opin. Decl. int. Commn zool. Nom. 19 (Opinion 516): 4, 5. There is no objective replacement name, but Hemming, 1958, ibidem 19 (Direction 96): (ix) stated the oldest available name associated with this species to be Castnia penelope Schaufuss, 1870, Nunquam Otiosus 1: 9, a conclusion he repeated in 1967, Bull. Br. Mus. nat. Hist. (Ent.) Suppl. 9: 98. In this catalogue we have adopted that name as the subjective replacement name for the type-species of Castnia Fabricius, 1807.
Castina Fabricius, 1807, was placed on the Official List of Generic Names in Zoology with Name No.659 in 1954, Opin. Decl. int. Commn zool. Nom. 4 Opinion 232.
Castnia penelope Schaufuss, 1870, was placed on the Official List of Specific Names in Zoology with Name No.1516 in 1958, ibidem 19 (Direction 96): (iv) and on page (v) of the same Direction Papilio icarus Cramer, 1775, was placed on the Official Index of Rejected and Invalid Names in Zoology with Name No. 520.
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