Descriptions of two new species of the genus Oligoaeschna from northern Taiwan, with notes on the status of the pryeri-group (Anisoptera: Aeshnidae)

2 syntopic new sp. of the pryeri-group Oligoaeschna, O. lieni sp. n. (holotype S: Tsaopi bog, 850m, Yuanshan, Ilan county, northern Taiwan, ll-V-1997) and O. tsaopiensis sp. n. (holotype <5 : Tsaopi bog, 850m, Yuanshan, Ilan county, northern Taiwan, ll-V-1997) collected from northern Taiwan are named, described and diagnosed. Relationship amongst the members of eastern Asian p/yen-group is discussed and inferred mainly from their male penile structure. With regard to male penile glans structure, the pryerigroup is considered to be the extant sister-group of the nearctic genus Gomphaeschna.