Butler (1884) wrote that he had received material from the Challenger expedition from the islands of St. Thomas, Bermuda, Rat Island, Ké Dulan, Ternate and Amobina, and mentioned that the first two are in the New World and the rest in the Old World. In this work he then described the species Catochrysops trifracta based on two damaged male specimens, and gave the type locality as “Rat Island, Strait of Malacca, 1^st September, 1873”. He provided the following description: “Deep lilac, the thorax above blue-black; head white; palpi with the terminal joint and a dorsal line black; abdomen blackish grey: wings below much as inC. cnejus, but differing noticeably in the fact that the series of spots across the disk of the primaries, instead of forming one slightly irregular stripe, are broken into three parallel oblique bifid white-edged brown dashes, one below the other; the secondaries also have only one subanal black spot with pale yellow zone, and barely perceptibly touched with metallic scales. Expanse of wings 23–28 millim”. Later on, Butler moved C. trifracta, C. cnejus (Fabricius, 1798) and several other species with “eyes quite smooth instead of hairy” to his new genus Euchrysops (Butler 1900), with C. cnejus as the type species. C. trifracta was briefly mentioned in Lepidoptera Indica (Swinhoe 1910) as a Malayan species allied to Indian species. De Nicéville (1890) and Seitz (1927) listed synonyms of Euchrysops cnejus (Fabricius, 1798), but E. trifracta was not among them. It was also not mentioned by Bethune-Baker (1923) in his revision of Catochrysops where Euchrysops also was revised, and synonyms for E. cnejus were listed. Additionally, it was not included in Corbet and Pendlebury (1934) and later versions of “Butterflies from the Malay Peninsula”. The name disappeared from use and eventually reappeared as a synonym of E. cnejus in Seki et al. (1991), which was followed by Bridges (1994) and subsequently by most online databases.

The two syntypes of Catochrysops trifracta are in the Natural History Museum, London (NHMUK), and the specimen in the best condition is shown in Figs 1 and 2. The locality label of both specimens say “Rat Island” and do not mention the Malaccas (Figs 3, 4, labels of same specimen as above). Thomson and Murray (1885) in their report on the Challenger expedition mention in a footnote on page 214 that the locality information given by Butler is incorrect, and that the specimens are actually from Ilha Rata (Rat Island) in the Fernando de Noronha archipelago off the coast of Pernambuco, Brazil. However, they mention that Catochrysops trifracta seems to be of Malayan origin. Kirby in Ridley (1890) in their work on the natural history of Fernando de Noronha found Hemiargus hanno (Stoll [1790]) (as Taurucus hanno), a species widely distributed in South America, to be frequent on Rat Island and the Main Island. In fact, this seems to be the only butterfly species occurring in the archipelago (Alvarenga 1962). Kirby further acknowledged that they had not seen C. trifracta (as Catachrysops [sic] trifracta) found by the Challenger expedition, but that this could be due to mislabelling of the specimens since the genus is only known from the East Indies. Butler (1900) was apparently aware of neither Thomson and Murray nor Ridley when he moved C. trifracta into his new genus Euchrysops.

Both syntypes are in relatively poor condition but it is clearly seen that these represent H. hanno. and not E. cnejus, nor any other Euchrysops. A non-type specimen of H. hanno from Venezuela (at the McGuire Centre for Lepidoptera and Biodiversity, MGCL) is shown in Figs 6, 7 since no type material of that taxon exists and no neotype of H. hanno has been formally designated (G. Lamas, pers. comm.). As in H. hanno, the C. trifracta specimens only have one black tornal spot (noted also by Butler as “only one subanal black spot”) with blue scaling towards the margin, and with a small amount of orange on the inner margin. In E. cnejus (Figs 8, 9, non-type specimen from the Philippines at MGCL) there are two black tornal spots with blue scaling, and both have a larger amount of orange on the inner margin. In E. cnejus these tornal spots are also visible on the upper side in both sexes, whereas in H. hanno and C. trifracta the single black tornal spot is hardly discernible. Furthermore, E. cnejus has a tail in the tornal area of the hindwing, which is lacking in H. hanno and C. trifracta. Finally, both H. hanno and C. trifracta have a grey sub-basal spot not present in E. cnejus, at the base of ventral hindwing cell Cu₂-2A. In the genus Euchrysops this spot is present in the widespread Afrotropical species E. malathana (Boisduval, 1833) and its sister species E. nilotica (Aurivillius, 1904) restricted to more arid parts of tropical Africa.

On these grounds, I place Catochrysops trifracta Butler, 1884 (syn. rev.) as a junior subjective synonym of Hemiargus hanno (Stoll [1790]). To fix the taxonomic identity of the name Catochrysops trifracta Butler, 1884 I hereby designate the following lectotype:

Lectotype male (Figs 1–4) in the Natural History Museum, London (NHMUK) with the following labels: Type; Rat Island 84 · 10 / Catochrysops trifracta type Butler; NHMUK010588635. An additional label “Lectotype Catochrysops trifracta Butler, 1884, male, M. Espeland 2022” will be added in due course.