PLATHEMIS., 205 
VV. Cross-veins immediately below the stigma none or one barely under 
the distal end, last antenodal of front wing continued to median vein, 
one (subnodal) bridge-cross-vein, arculus between first and second 
antenodals but nearer to first, sectors of arculus arising from a long 
common stalk, subnodal sector and supplementary sector next below 
separated from each other by only one row of cells, sectors of triangle 
of hind wing separated at origin ; spines on the third tibia 10-15 in 
each row, slender; genital hamule of male two-branched, vulvar lamina 
of female not projecting. . . . . . 1... ee). UPacnyprpnax. 
The extensive series of statistics on which this Synopsis is based show that all the 
venational features vary to some degree. Use has been made of these features, 
however, in cases where the variation from a given condition has not exceeded 10 
per cent. ; this variability renders it necessary to give a number of characters for each 
genus. ‘The statistics themselves, it is hoped, will be published elsewhere. 
The classification of the Libelluline is admittedly difficult. ‘There are probably a 
number of different lines of descent included within the group and no arrangement, 
such as a synoptical key necessitates, can do justice to these. However, several genera 
(e. g., Plathemis, Libellula, Ephidatia, Uracis, Tholymis, Perithemis), each of which 
retains some primitive characters simultaneously with the possession of specialized 
features, have been placed near the beginning of principal divisions of the synopsis. 
In some cases I have been obliged, in order to render the key useful for identification, 
to begin a rubric with some character of less importance, but possessed by both 
sexes, when the most important feature is found in only one sex; this applies 
particularly to rubrics F, FF, G, and GG. 
As in the other generic synopses in this work, the characters of each genus have 
been placed, as far as possible, in an order from less to greater variability. 
PLATHEMIS. 
Plathemis, Hagen, Syn. Neur. N. Amer. p. 149 (1861) ; Kirby, Trans. Zool. Soc. Lond. xii. p. 287 
(1889) ; Cat. Odon. p. 28 (1890). 
1. Plathemis subornata. 
Plathemis subornata, Hagen, |. c. p. 149 (1861)*; U.S. Geog. Surv. Terr. (Wheeler’s) v., Zool. 
p. 919 (1875) *; Proc. Bost. Soc. Nat. Hist. xviii. p. 68 (1875) *°; Proc. Davenp. Acad. Nat. 
Sci. i. p. 204 (1876)*; Banks, Trans. Amer. Ent. Soc. xix. p. 855 (1892) °; Needham & 
Cockerell, Psyche, x. p. 189 (1903) °. 
d. Ventral plate on abdominal segment 1 bifid for its distal half only (instead of entire length as in P. lydia), 
the branches wider, separated by an angular interval of about 90°. Most of the basal half of the wings 
not occupied by fuscous and the abdomen becoming pruinose with age. 
Abdomen *, 3 26-28°5, 9 22-25; hind wing, ¢ 2, 32-35 mm. 
* The length of the abdomen as given throughout the Libelluline includes the appendages, 
BIOL. CENTR.-AMER., Neuropt., Octoder 1905. Ie 
