1863.] 
269 
to texana^ which likewise has only 2—3 ranks of cellules on the post¬ 
costa of the front wing, and in which the proportions of the front wing 
are 30 and 5, may not improbably belong to americana. If propor¬ 
tioned exactly as in americana 9 the front wing would be 5.09 mill, 
wide. 
As I still think from the structure of the postcosta of the front 
wing, and the greater comparative breadth of that wing, that the 9 
formerly sent me by Mr. Uhler as 9 Americana belongs to pseudame- 
ricana^ it is probable that both these two species exist in Mr. Uhler’s 
neighborhood, and that he may have partially confounded the two to¬ 
gether in his description of the former. I doubt the fact of the prin¬ 
cipal sector &c. in % americana being “whitish’’ beneath in the tene- 
ral individual, as stated by Mr. Uhler, when I see with my own eyes 
that it is perfectly black, not brown, in the adult specimen. Still, 
coloration in Agrionina is so variable, that it is difficult to fix the limit 
of variation. 
It will be observed that, according to Mr. Uhler, it is only the tene- 
ral % and the teneral and semiadult 9 9 of americana that have the 
principal sector &c. whitish beneath; whereas in pseudamericana % 9 
and texana % the adult specimen also has these veins whitish beneath. 
Pseudamericana % differs also both from % americana^ % scelerata 
and % texana^ in the tubercle behind the laminiform tooth (not the 
one on its superior base) being only about 1 as wide as that tooth, 
instead of about ^ as wide as in americana and scelerata^ or 1 as wide 
as in texana. 
On p. 217 I said that “in Gromphus there are normally two dark 
stripes on the pleura, one on the mesothoracic epimerum and one on 
the metathoracic episternum.” The locus of the latter is, correctly 
speaking, on the anterior suture of the metathoracic episternum, or, in 
other words, on the suture dividing the meso- from the meta-thorax. 
In many, perhaps'all, Agrionina and Calopterygina, (Agrion, Lestes, 
Calopteryx, Hetserina, Libellago, &c.) there exists behind the humeral 
suture a more or less developed supernumerary or false pleural suture 
dividing the mesothoracic epimerum into two subequal parts, the pos¬ 
terior part bearing the spiracle. Slight traces of this suture are occa¬ 
sionally found in the other four Odonatous Sub-families. The Mono- 
