Update 2: I've added a few new images (marked "NEW IMAGE:") that emphasize the mesepisternal and thoracic suture features. plus a couple of uncropped flight pics to show its foraging height:
Update: I received feedback from various experts, and those who have expressed an identification have all gone for C. apeora - an apparently rare species known from Veracruz (and probably Nuevo Leon), Mexico southwards into Central America (and probably Cuba) that Dennis Paulson described in 1994 along with a similar taxon, C. diapyra, with a similar known range (see Odonatologica volume 23 pages 379 - 392). It seems that this individual is definitely one of these two taxa, and that all visible features favor apeora. Here are the relevant ID features, as I understand them from talking to Dennis and studying the few photos I've been sent of these two taxa:
1) Front of thorax: apeora has a brown stripe/mark of variable length on each mesepisternum (= the two thoracic plates behind the eyes that are otherwise all green, separated by a narrow brown carina); diapyra lacks any brown marks on the mesepisterna.
2) The frons (= top of head in front of the eyes): female apeora has a thickish-based black T-spot that does not change with age; female diapyra starts as a teneral with a black T-spot (possibly the central base is thinner than on apeora) but soon (how soon?) has this fade or change color such that it largely disappears, resulting in an almost uniform frons on adult females.
3) Lateral thoracic sutures (= two main plate join-lines on the side of the body): apeora has a thin but obvious brown line along both sutures, with the anterior line being very slightly thicker in the dorsal half, while the posterior line is very slightly thicker on the ventral half; diapyra has virtually
no color along these sutures, showing a hairline that is very slightly more prominent on the upper third of the posterior suture. Fresh teneral individuals of diapyra can have the suture lines slightly more visible, but probably not to the extent typical of apeora.
4) Flight: apeora is Greek for "flying on high" - so-named by Dennis because of this taxon's habit of flying almost constantly, and at tree-top level or higher; diapyra typically flies much lower and is much easier to net than apeora.
5) Size:
apeora is significantly larger than diapyra; apeora is roughly similar to Regal Darner C. ingens in size.
- there may be other subtle features that have yet to be worked out; the differences in the underside of S8 - S10 are not visible in any images of these taxa known to me.
I've changed the embedded text below to reflect this new situation:-
This female Coryphaeschna darner was photographed April 15, 2008 c.4 miles east of Santa Ana NWR on the north bank of the Rio Grande, Hidalgo county, Texas; it spent most if its time feeding in a c. 30 yard "beat" at tree-top height (or above), just twice briefly dropping down to above head height; it perched once - 20+ feet up - for c. 45 seconds; it was a large darner - I estimated its length to be between Swamp and Regal Darners (E. heros and C. ingens) - two species i'd seen in a feeding swarm the week before in east Texas:
The shape of the lower-base of the hindwings clearly make it a female...
... but the full-length petiolate cerci are very short-looking for this genus.
Note in the image below, the (arrowed) brown elongate mark in the center of the mesepisternum (green panel on the lateral-front part of the thorax); also note (arrowed) the brown lower end of the posterior thoracic suture:
NEW IMAGES: The two images below are from two seperate originals to the one above - each at a slightly different angle - yet all three clearly show the mesepisternal mark:
note that in the image below - at a different angle to the one above - the brown mesepisternal mark has been drastically foreshortened and has disappeared into a shadowed area; note above and below the prominence of the T-spot on the frons, and the thickness of the black base of the "T":
NEW IMAGE: A new version of the above photo that shows the mesepisternal mark (here at its least-visible angle and in shadow):
It is clear that the pattern of the thorax rules out C. ingens and teneral female C. adnexa (which have wider brown stripes, almost like those of C. ingens - per photos by Michael Veit and Tom Langshied):
- and a closer look reveals the brown mesepisternal mark visible above the end of the folded foreleg, plus the thin but obvious brown lines along the thoracic sutures:
NEW IMAGE: Better-showing the brown mesepisternal mark extending beyond the folded foreleg (also note the thoracic suture lines):
Note that the cerci, when "folded-back", do not reach the joint suture of S8/S7:
note also that the wings completely lack any hint of coloration:
above is the original; below a zoomed-version adjusted to reveal more detail in the shadows:
notice again how short the cerci look in the flight images:
above is the original; below a version adjusted to reveal more detail in the shadows:
NEW IMAGES: Here are two shots to show the typical flight height of this darner:
