Hemming (1967) stated:-
(a taxon (a) bearing a name proposed to be validated by the Commission under the above Powers and (b) having, by similar designation, as the representative of its holotype the specimen figured by Horsfield as fig. 2 on plate 1 in the work cited above).
The genus Pithecops Horsfield was established on the basis of a misidentified type-species in circumstances which are very unusual in the sense that Horsfield's mistake, which has been followed by all subsequent authors and is still currently followed, only came to light in 1940. The circumstances attending this case are set out below.
As established by Horsfield, the genus Pithecops contained one nominal species, Papilio hylax Fabricius, 1775 (Syst. Ent. : 526), which he described and figured (: 66, pl. 1, fig. 2) and, as pointed out by myself in 1934 (Gen. Names hol. Butts 1 : 105-106), four other species mentioned incidentally as belonging to this genus. Scudder in 1875 (Proc. amer. Acad. Arts Sci., Boston 10 : 252) overlooked these latter species and erroneously considered that Papilio hylax Fabricius was the sole included species and therefore the type-species by monotypy. This misconception on his part does not however invalidate his action in stating that Papilio hylax is the type-species of this genus.
Between the publication by Fabricius of the name Papilio hylax and the appearance of Horsfield's book in 1828 that name was used by only two authors ; these were, first, Donovan (1800, Ins. India : pl. 46, fig. 2) who published a crude figure which is unrecognizable, and second, Godart (, Ency. méth. 9 (Ins.) (2) : 701), who also came to the conclusion that, as described by Fabricius, this species was unrecognizable. The next author to use the specific name hylax was Horsfield who gave an excellent figure of the well-known species found from Sikkim to Burma, figured most recently by Evans in 1932 (Ident. Ind. Butts : pl. 27, fig. 16/2). This interpretation of Papilio hylax was followed by every subsequent writer until in 1940 (Entomologist 73 : 276) it was shown by Corbet to be absolutely incorrect In writing his note on this subject Corbet was assisted in having had access to a specimen in the Copenhagen Museum labelled "hylax" in what the authorities of that Museum believed to be the handwriting of Fabricius. This syntype was shown by Corbet to be a specimen of Lycaena gaika Trimen, 1862 (Trans. ent. Soc. Lond. (3) 1 : 403), a species which by original designation is the type-species of the genus Zizula Chapman, 1910 (Trans. ent. Soc. Lond. 1910 : 483). Corbet concluded his paper by noting that the oldest available name for the taxon dearly described and figured by Horsfield under the misapplied name hylax Fabricius was corax Fruhstorfer,  (Pithecops hylax corax Fruhstorfer, , Arch. Naturgesch. 83 Sect. A.1 : 79).
If the changes in nomenclature necessitated by Corbet's determination of the true identity of Papilio hylax Fabricius had been put into effect, the results would have been disastrous, leading to the most serious confusion both at the genus-name and at the species-name, levels. These may be summarised as follows :
(a) The species hitherto universally but incorrectly known by the specific name hylax Fabricius would in future have had to take the almost unknown name corax Fruhstorfer, .
(b) The species hitherto known by the well-known name gaika Trimen, 1862, would in future have had to take the name hylax Fabricius, which had never previously been applied to it.
(c) The species hitherto incorrectly known as "hylax Fabricius" with its name changed to corax Fruhstorfer would have been placed in the genus Eupsychellus Röber, 1891, with the type-species of which (Lycaena dionisius Boisduval, 1832) it is subjectively regarded as being congeneric.
(d) The name Pithecops Horsfield with the true Papilio hylax Fabricius (a senior subjective synonym of Lycaena gaika Trimen) as its type-species would have replaced the name Zizula Chapman, 1910, of which Lycaena gaika is the type-species.
(e) The genus Pithecops, as hitherto interpreted as having the false "hylax Fabricius" of Horsfield as type-species, is currently treated as belonging to the subfamily Everinae Tutt,  of the family Lycaenidae, while Zizula Chapman is considered to belong to a different subfamily which Stempffer has named Brephidiinae (type-genus : Brephidium Scudder, 1876). If the changes indicated in (c) and (d) above were to be put into effect, the genus Pithecops would need to be transferred from the subfamily Everinae to the subfamily Brephidiinae.
While it was evident that a continuance of the practice of ignoring the position under the Code of the generic name Pithecops Horsfield and of the species name Papilio hylax Fabricius would be indefensible, it was evident also that it was essential in the interest of nomenclatorial stability to seek the assistance of the Commission in securing a solution of the problem which would prevent the devastating changes in existing nomenclatorial practice which would result from the application in this case of the ordinary rules in the Code. What was chiefly needed was an arrangement which would both (i) avoid the transfer of the specific name hylax from the species to which it was applied by Horsfield nearly 140 years ago and has been applied ever since to a species to which it had never been applied and (ii) would avoid a corresponding change in the application of the generic name Pithecops Horsfield. It was finally concluded that the best course would be to request the Commission to use its Plenary Powers (a) to suppress for the purposes both of the Law of Priority and of the Law of Homonymy the specific name hylax Fabricius, 1775, as published in the binomen Papilio hylax, (b) to validate the name Pithecops hylax, as published by Horsfield in 1828, the taxon so named to have as its holotype the specimen figured by Horsfield in 1828 as figure 2 on plate 1 in the work referred to above, and (c) to designate the nominal species Pithecops hylax Horsfield, , as validated in (b) above, to be the type-species of the genus Pithecops Horsfield, 1828. In accordance with the provisions of Article 80, the foregoing arrangements are here adopted provisionally, pending a decision by the Commission on the application submitted.
Cowan (1968: 7) stated:-
Opinion 822 NEGATIVED the List [Hemming, 1967] forecast in ruling that; Pithecops Horsfield is to have as type-species Pithecops corax Fruhstorfer (1919) (as published in the combination P. hylax corax), Arch. Naturgesch. 83 (A) (1) (1917) : 79.
It should be noted that corax Fruhstorfer is now regarded as the Javan subspecies of P. corvus Fruhstorfer (1919 : 79), hylax Fab., 1775 having been identified as the older name for Zizula gaika (Trimen).
Pithecops corax Fruhstorfer  was designated as the type-species of Pithecops Horsefield,  using the plenary powers of the Commission. Pithecops corax was placed on the Official List of Specific Names in Zoology, (Opinion 822), The Bulletin of Zoological Nomenclature, 24 (4) : 216. Pithecops was placed on the Official List of Generic Names in Zoology.
The higher classification used here follows Lamas (2008).
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