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The new sp. from the central Kalimantan province of Borneo is described and figured. The original type series of R. cucullata Selys was examined and a 3 specimen is designated as lectotype. The single 9 syntype is shown to in fact be R. humeralis Selys. The true 9 R. cucullata is described and figured for the first time. Significant characters of R. aurofulgens Laidl. are figured for comparative purposes. Keys are provided to both sexes of the three species, comprising the extended cucullata group of F.F. Laidlaw (1950, Trans. R. ent. Soc. Land. 101: 233-269).

Both sexes of the new sp. are described from Brunei (holotype 6: Belait distr., Sungei Lumut, I6-X11-I995; deposited in RMNH, Leiden), and notes on its ecology and behaviour are provided. This is the second sp. of the hitherto monobasic genus, widespread in Sundaland.

Territorial and courtship displays and their relation to male ornamentation were examined in 11 spp. in N Borneo. Males of all spp. were territorial, guarding a small area of oviposition substrate and attempting to mate with ovipositing females. Most spp. exhibited a ritualized threat display, in which males faced each other and displayed the terminal markings on their wings. In the genus Libellago there was a pronounced stationary wing display, in which the outstretched forewings were held completely still for about a second. This behaviour did not occur in L. hyalina which lacks markings on its wings. Apart from L hyalina, some form of courtship occurred in all spp. for which information was available, typically involving the male swinging to and fro in a semicircle to the side of the female, while displaying and vibrating his pruinescent legs. Variations included display of various markings on wings and abdomen, probably associated with species recognition, and in Rhinocypha aurofulgens, standing on the substrate during courtship, a modification probably associated with loss of pruinescence on the legs in this spp. Interspecific interactions were frequently intense, and probably have been important in the evolution of displays. An outline of possible evolutionary relationships among display elements is suggested.

Pericnemis triangularis Laidlaw (Coenagrionidae), Indaeschna grubaueri (Forster) (Aeshnidae) and Lyriothemis cleis Brauer (Libellulidae) are reported breeding in phytotelmata in the understorey of lowland mixed dipterocarp rainforest in Borneo. The pattern of utilization by the 3 spp, of phytotelmata of varying sizes is surveyed and observations are made in field and laboratory on larval behaviour, especially territoriality and intra- and interspecific predation, and developmental rales. Possible adaptations to special conditions found in phytotelmata, including low oxygen tensions, limited food and close proximity of other larvae, are discussed. Descriptions are provided for the larvae of P. triangularis and I. grubaueri.