Type species: catamitus Geyer.
Synonyms: Cleosiris Boisduval (type species catamitus); Agonis Felder
(type species lycaenoides Felder).
The clearest distinction between the two Bornean calliduline genera lies
in features of the male abdomen. The facies in both is diverse and
provides no definitive features, nor does the venation (illustrated for
several taxa by Pagenstecher (1887)).
In male Tetragonus the hair-pencils, or culcita (Kobes, 1990),
extend in broad patches laterally between the eighth tergite and the
seventh segment, with the intersegmental membrane much expanded. The
eighth sternite is narrow, elongate, bifid at each end, especially
basally, somewhat resembling an old-fashioned clothes-peg. In the
genitalia the saccus is diagnostically bifid. The aedeagus is relatively
larger than in Callidula, with the cornuti stronger.
In the female of the type species the apodemes of the eighth segment are
moderate. There is a large, ovate, scobinate signum and some corrugated
sclerotisation in the neck of the bursa.
The biology of the type species is described below.
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