278 MK. W. F. KIRBT— A EEVISION OF 



with 5-10 antenodal nervures and 6-12 postnodal nervures, the first two or three 

 subnodals not continuous, triangle free, its base nearly coinciding with the arculus, 

 followed by two or three rows of cells, no supratriangular nervures, one cross nervure 

 in the lower basal cell, sectors of the triangle united at the base (separated in T. trivialis 

 and some other species): anal appendages of the male as long as the last two segments, 

 depressed, the lower appendages nearly as long as the others, appendages of the second 

 segment not very conspicuous; appendages of the female rather long; vulvar scale of 

 the female ver}' variable, in typical Tritlumis hardly perceptible, but in some of the 

 American species which approach Erytlirodiplax (a genus which 1 regard as at present 

 only provisionally distinct) it is nearly as prominent as in Crocothemis. 



Type Libellula aurora, Burm. 



I find it necessary, after separating several discordant species from Trithemis under 

 other names, to include in this genus, at least provisionally, (1) the tropical Old-World 

 group usually placed in Diplax, of which LibeUula trivialis, Ramb., is the type ; (2) a 

 number of American species included by Hagen in Biplax {Sijmpetrum), but distin- 

 guished by their more numerous and more crowded costal nervures, and generally by 

 the variable number of posttriangular cells; and (3) most of the species placed in 

 Erytlirodiplax by Brauer. 



Genus 23. Eeythrodiplax. 

 Brauer, Verli. zool.-bot. Ges. Wien, xviii. pp. 368, 722 (1868). 



Characters of Trithemis. Wings short; abdomen very short and thick, slightly 

 thickened at the base, otherwise almost equally broad throughout ; anal appendages 

 of the male unusually small (as long as the ninth segment) and depressed ; the middle 

 appendage a little shorter than the others; appendages of the second segment very 

 conspicuous. From Erythemis, which it much resembles, it may be distinguished by 

 the convex frontal tubercle, the very short broad body, hardly tapering even at the 

 extremity, and the slender spines on the legs. The vulvar scale of the female is very 

 prominent. 



Type Libellula pleheia, Ramb. (= corallina, Brauer). 



Genus 24. Be.\chtthemis. 

 Brauer, Verh. zool.-bot. Ges. Wien, xviii. pp. 367, 736 (1868). 



Frontal tubercle large, distinctly conve.\ above ; eyes contiguous in front ; abdomen 

 rather stout, cylindrical, thickened at the base, and gradually tapering, shorter than 

 the hind wings, segments 2-4 carinated, segment 8 not perfoliate in female : wings short, 

 pterostigma rather long ; fore wing with 7-8 antenodal nervures and 6-7 postnodals, 

 the last antenodal and the first three postnodals not continuous, cells of the postnodal 

 area simple, triangle moderate, traversed (exceptionally free), the base slightly oblique, 

 followed by three rows of cells, increasing, no supratriangular nervures, one cross 



