302 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
sides of the eighth abdominal segment not dilated (i. e. not “ per¬ 
foliate,” Kirby) in the females; vulvar lamina not prolonged, but 
with a median excision. 
The chief peculiarity of these five genera, however, is the modi¬ 
fication of the armature of the second and third femora in the 
males , and of the tarsal nails in both sexes. The details of the 
modifications are characteristic for each genus, Dythemis being the 
least, Macrothemis the most modified of the five (PI. l,figs. 1-12). 
All these genera are confined in their distribution to the warm 
parts of America. 
Variations from the above Common Generic Characters. 241 
individuals,— 33 29 9 Dythemis, 8 J 2 9 Paltothemis, 17 $ 15 9 
Brechmorhoga, 6 $ Scapanea, 76 $ 55 9 Macrothemis, — have 
been specially examined for the present paper. Special attention 
was paid to recording variations, in Baja Californian representatives 
of these genera, in Proceedings of the California academy of 
sciences, (2), vol. 4, p. 463, 467, et seq ., so that those data are also 
available. 241 individuals, however, is the basis on which all of 
the following percentages have been calculated, except where refer¬ 
ence is expressly made to this last quoted paper. The variations 
noted from the preceding common characters have been : — 
Supra-triangulars. One in the left front wing of one Brechmo- 
rhoga mendax female, .104 %. 
Last antenodal on the front wings continued to the median vein 
in right front wing of one B. nubecula female, .207 %. Of 91 males, 
62 females of Dythemis sterilis, two females had this last antenodal 
continued, in one wing only, in each case (Proc. Cal. acad. sei., 
(2), vol. 4, p. 524), .654 %. Total, .381 %. 
Sectors of triangle in hind wings a little separated at origins, on 
one side only in one female D. rufinervis , one female D. velox , one 
female Macrothemis mdgipes , one female M. tessellata ; on both 
sides in one female M. mdgipes , two males M. inequiunguis , one 
female M. tessellata , 2.49 %. 
It is of interest here to note that, while the total numbers of 
males and females examined for all these characters are 140 and 
101 respectively, the females offer a greater number of variations 
than the other sex, the percentages of variations in the variable 
characters being .357 (<£) and 1.238 (9 ). 
The Differences between the Dive Genera are shown in the fol¬ 
lowing table:— 
