Platylestes heterostylus, M.A. Lieftinck, 1932

M. A. Lieftinck, 1932, Two new species of Odonata from Java, Stylops 1 (11), pp. 248-253 : 248-251

Platylestes heterostylus , sp. n. ( figs. 1 - 2 ).

Material studied: — One ♂, adult, South W. Java; res. Banjoemas, Djeroeklegi, 28. i. 1931 (F. C. Drescher) . “ Head and eyes dark brown. Thorax grass-green with black spots. Abdomen grass-green with black rings at articulations. Appendages white. ” (Living colours.)

Closely related to platystylus , Laidlaw (? nec Rambur).

♂ (colours somewhat faded).— Labium yellowish. Labrum, anteclypeus and genae olive-green; postclypeus also green but with three indistinct brownish spots above.

Ground-colour of head a dark olive-green, conspicuously marked with black in the centre and between antennae and the eye-margin. Small greenish spots around each lateral ocellus. Postocular lobes dark olive-green, decorated with cloudy black markings. Occiput clear greenish-yellow.

Pro- and syn-thorax olive-green above, pale greenish to ochreous on side and underneath. Prothorax with a median black spot at base of anterior lobe and a double fascia of the same colour over its middle.

Synthorax with a dark brown, somewhat triangular, spot along dorsal fifth of median Carina, and with four series of black dots on either side of it, irregularly spread over the mesepisterna and the thoracic sides, as is shown in fig. 1 .

Legs yellowish-green with two narrow, reddish-brown, stripes along exterior sides of femora, and with a similar brown stripe along inner and outer sides of tibiae. Spines, tarsal articulations and claws black.

Wings hyaline. Neuration in basal part reddish-brown, otherwise black in colour. Pterostigma short, a little inflated at the middle of its length, jet-black, its inner and outer margins narrowly white. The venation is almost wholly identical with that of the wings in a male specimen from Calcutta (India), photographed by Laidlaw (1920, Rec. Ind. M us., 19: 156, fig. 4), except in a few points that may be tabulated as follows:—

1. The nervures M s and M 3 are separated at their origin for a distance equal in length to the first cross-vein between them.

2. In hind-wing the nervure M 3 is at first straight, thence, after a distinct costad convexity at the level of the seventh postnodal cross-vein, is shallowly concave, and finally is again somewhat convex just before reaching the wing-margin.

3. The pterostigma of front wing is exactly one and a half times longer than wide, that of hind-wing being a shade longer. Inner and outer margins run parallel to each other in both pairs of wings.

Abdomen grass-green, with the articulations finely -black, and marked with warm dark cinnamon-brown as follows:— Segment 1 has a mid-dorsal marking of that colour and a black point on the middle of the sides, the side-portion of articulation between first and second segment being likewise black. Segm. 2 has a dorsal brown marking, strongly constricted at middle, and an anterior and posterior pair of very small, diffuse, dark brown spots on either of the mid-dorsal carina; sides with a very distinct, oval, black dot situated beyond the middle of segment. Segm. 3-7 have cinnamon-brown markings covering the whole dorsum but strongly tapering in front and, after being gradually narrowed to behind, are suddenly and conspicuously widened before the end; the posterior figures thus formed enclose a minute, transversely placed, black dorsal stripe, and are narrowly attached to the black articulation. The brown marking on dorsum of segm. 7 deepens gradually in colour to its apex, and 8-10 are dark blackish-brown; 8, 9 and 10 have an ochreous dorso-lateral spot about at their middle, and 8 has a comma-shaped yellow marking along side at base. Lower apical third to half of the tergites of segm. 7-9 black.

Anal appendages of very characteristic shape. Sup. apps. equal in length to segm. 8; basal fifth deep black, the rest of their length pale yellow; apices rather suddenly and strongly bent inwardly, the points covering one another. On the inner side, at the end of the first third of their length, is a blunt projection, and, slightly beyond this, there is a triangular cone, directed straight downwards; besides, at the end of the second third, the sup. apps. are provided with a sharply pointed tooth directed backwards and inwards. Inferior appendages brown at base, fading to yellow distally; over two-thirds the length of superiors, meeting each other apically but with the points knob-like and only scarcely upturned, not spatulate; each carries at its base on the inner side a tubercular projection for over one-third of its length ( fig. 2 ).

Length: abd. + apps. 36, hind-wing 21∙5,pt. 0∙9/1∙0mm.

The specimen is the holotype.

The genus Platylestes, Selys , heretofore containing only a single rare species, platystylus (Ramb.) in Bengal and Burma, has been thoroughly discussed by Laidlaw (loc. cit., pp. 155 - 157, figs.), and, more recently, by Fraser (1930, J. Bombay Nat. Hist. Soc., 34: 92 - 94, figs.).

To the characters distinguishing the genus from Lestes , and enumerated by Laidlaw, I have nothing to add, the species described in this paper from Java agreeing very well in all important generic characters with the Indian species. According to Fraser, who described the supposed second known female of platystylus (taken in Bengal), his specimen differs considerably from the original description of the type as given by Rambur, so that it still remains an open question as to whether Laidlaw’s and Fraser’s insects are identical with the true platystylus or not. Only two males are known: one from Calcutta, the supposed allotype, and one from Burma.

The occurrence in Java of a second species may well be regarded as of exceptional interest, as its ranging so far south-eastwards means a welcome addition to our knowledge of the distribution of the genus. In all probability more representatives will be discovered sooner or later in the interjacent regions, although both species seem to be inconspicuous and very rare insects.

The principal differences between the males of ' platystylus and heterostylus may be given as follows: —

platystylus .

1. Abdomen 33∙5, hind-wing 21 mm.

2. Thorax palest khaki-brown above, milky-white on side. Venter powdered with white. Black spots along ventral margin of metepimerum apparently absent.

3. Pterostigma with costal side decidedly shorter than anal side, inner and outer margins divergent.

platystylus .

heterostylus :

4. Sup. anal apps. curling in at apices to meet each other in a gradual and regular curve, but the extreme apices curling a little outwards again. Inf. apps. half as long as upper pair, their distal half after a slight constriction a little widened, and gently curved inwardly to- wards apices, which are more spatulate at tip.

heterostylus .

1. Abdomen 36, hind-wing 21 - 5 mm,

2. Thorax olive-green above, paler along sides (grass-green in living male), not pruinose below. Two addi­ tional black spots along ventral margin of metepimerum.

3. Pterostigma with costal side equal in length to anal side: hence inner and outer margins parallel to each other.

4. Sup. anal apps. less slender, with sub­ median interior acute tooth placed more distad, apical third of each rather abruptly inwardly bent and overlapping each other in a trans­ verse plane, extreme apices thus curled distinctly inwards. Inf. apps. over two-thirds the length of upper pair, straight and slenderer, with tips rather club-shaped and rounded ( fig. 2 ).

Figures

Fig . 1.— Platylestes heterostylus, sp. n. Diagram of thoracic colour-pattern.

Fig . 2.— Platylestes heterostylus, sp. n. Male anal appendages, dorsal view and right side.