[October 
23-^ 
of a pale yellowish brown color, and with the 3 stripes bright green instead of 
black, and the anterior stripes much more abbreviated above. Antealar sinus 
with a small pale brown spot in the anterior angle. 4^/i. The abdomen is, as 
usual, shorter and stouter, and it is more tinged with brassy except when ob¬ 
scured by pruinescence; and there is a distinct, narrow, basal, whitish annu¬ 
lus, interrupted above, on joints 3—7. Joints 1—2 are laterally pale-reddish- 
brown, dorsally grass-green, joint 2 with the sides of the green spot very deeply 
emarginate in the middle. Joints 3—10 laterallv marked with obscure pale 
brown, 10 carinate for its entire length, the carina tipped with a slender, acute 
thorn, beneath which is a pale tubercle, and having on each side of its tip a 
minute acute tooth, bth. The femora, except towards the tip, are very pale- 
brown ‘^interiorly” and “posteriorly,” the posterior brown surface with a lon¬ 
gitudinal row of dusky dots. &th. The wings are entirely immaculate, lightly 
and uniformly subflavescent, but rather more obviously so at the extreme base 
and occasionally along the costa. Veins and cross-veins all black. Pterostigma 
white, li— '2^^ times as long as wide and surmounting li—1-| cellules. The ab¬ 
dominal appendages are ^ as long as the last abdominal joint, robust, conical, 
excurved and tapered to an acute thorn at tip, black at tip and brown towards 
their base. Antecubitals 17—21. Postcubitals 22—28. Cross-veins of basal area 
(front wing) 4—5. Of quadrilateral (same) 3—5. 
Length % 46^—51 mill. 4:2 —44 mill. Abd.—411 mill. 9^3—34 mill. 
Exp. 56—59 mill. 9 —32 mill. Front wing % 29—31i mill, its width 6—61 
mill, 9 31—32 mill, its width 6^—6^ mill. Hind wing % 28—30 mill, its width 
51—6 mill. 9 30—31 mill, its width 6—6i mill. 
Thirty-six % , four 9 j three pairs taken in coifu. Occurred on Rock 
River, Ill., whence the trivial name, from the middle of August to the 
middle of September. Local and not very common. Rupinsidensis 
Walsh, occurred on a small rivulet emptying into the Mississippi 
River three miles from the nearest point on Rock River. Rupamnen- 
sis scarcely dilfers from that species except in the spot on the % front 
wing being partly carmine-red, in that spot always extending much 
behind the postcostal vein, in the basal spot on % hind wing being 
very much darker, and in the coloration of the femora. The S abdo¬ 
minal appendages are undistinguishable, and I should have supposed 
rnpmsidensis to be the immature form of rupamnensis but for the fact 
that my unique % specimen of the former is decidedly mature, and 
that, although many of my 36 % specimens of the latter are immature, 
yet none of them show any approximation whatever to the other spe¬ 
cies in the coloration of the basal spot of the front wing. The differ¬ 
ence in locality is not so slight as might at first sight be supposed. I 
have observed that Hetserina 9 fiirts her eggs into the open river, with¬ 
out attaching them to aquatic plants ckc., as do certain other Odonata; 
