Identification Synthemids are often encountered and initially confusing. They do however perch quite regularly, their flight is quite slow and they are often found in very localised habitats such as small creeks or springs and seepages in forests, so catching is usually quite easy. 

A good binocular view of most however may be enough to identify them to species. Only one species, Archaeosynthemis orientalis, is brown and the rest are largely black. They are relatively small thin dragonflies with yellow spots forming bands down the body. Most have bright green eyes. If you are catching these insects and photographing them to key them out, it is best to pay attention to wing venation, the pattern of the face (front, sides, top and underneath), the pattern of abdominal markings and in the case of females, the profile of the tail tip showing the position of the ovipositor.

For field identification, the first thing to look for is whether the insect has yellow spots at the base of each wing. There are four in all, as shown by the red arrows in this illustration -

Species that have these spots are: Parasynthemis regina, Eusynthemis brevistyla, Eusynthemis virgula and Synthemis eustalacta. 

P. regina is a very distinctively marked dragonfly. Males have groups of pale spots that surround  black diamonds down the dorsal mid-line of the abdomen and a pair of very large tail spots. On other boldly marked species such as S. eustalacta, the forward-most spots on each band decrease in size and almost disappear towards the tail so the last band comprises just two spots. E. brevistyla is a relatively small, thin lowland species with very indistinct spotting except for the tail marks. E. virgula is  unique in being the only species that has spots on the top of the thorax, whereas all other species have dark thoraxes with a yellow line down the middle, as illustrated below.

If no spots are visible at the wing joints, then the insect is either Eusynthemis tillyardi or Eusynthemis guttata. E. tillyardi or 'Mountain Tigertail' is found near upland swamps and the upper reaches of small streams whilst the relatively common E. guttata is found in lowlands and foothills. Both species have a regular series of similarly sized bands in the middle of each segment, each band comprising just two spots. To be certain in identification, E. guttata has a dark lower mandible (A) (pale in E. tillyardi) and a straight synthoracic stripe (B) (distinctly curled in E. tillyardi). These features may be visible in the field through binoculars.

The following figures illustrate the dorsal abdomen patterning of males of the species