Anyway, it is Ophiogomphus sinicus. A rather weird Ophiogomphus at that. It was first included in Onychogomphus as Onychogomphus sinicus, but after studies were done on the larval stages, it was transferred. Well, I guess there are good reasons to do so, but it sure as hell does not look like regular Ophiogomphus species. It is known from a large part of Southern China, although locations are scarce, for instance Guangdong and Guangxi. Not too surprising it occurs in Northern Vietnam.
|Ophiogomphus sinicus, male, perched on rock in stream|
|In hand, the same male|
|Face of O. sinicus. There is not much difference with Lamelligomphus, really|
|Appendages in dorsal view|
|And in ventral view. Note the dorsal tooth at 1/3rd of superior and inferior appendages|
|And to be complete, ventral view|
|The shape of the anterior and posterior hamuli|