1863.] 
263 
Gr. GOMPHUS AND ITS AMERICAN SUBGENERA. 
Subgenera. 
Inferior % I 
abdominal \ 
appendages -J 
not divari- 
eate. j 
I 
Inferior 
abdominal 
appendages 
widely di¬ 
varicate. 
Stripes of the thoracic dorsum more or less 
obsolete J legs short; occiput ^ 9 Erpetogomphus.’ 
armed. 
Stripes of the thoracic dorsum distinct; ] 
legs long; occiput'^ unarmed, occiput > Ophiogomphus.* 
9 with large horns. j 
f Abdominal joint 9 at j 
least ^ as long again 
as 8 ; 10 very short, 1 MACRoroMPHns t 
from W of 9. Ear- h ^^crogomphcs.T 
lets 9 subobsolete 
, as usual. 
manotprolon- 9 
ged; vesicle of g . „ 
about half as long as 
9. Earlets of 9 
large as they com¬ 
monly are in Gom- 
phina. 
Internal vein of f Abdominal joint 9 a- 
the pterostig- I bout equal to 8 ; 10 
ma prolonged | half as long as 9 or j’ 
as usual; vesi- less. j 
cle of thever- Abdomen with joints \ 
8—10 gradually di- 
[ minishing in length. 
Internal vein of 
the pterostig- 
the vertex se¬ 
mi-circular. 
tex straight or 
nearly so. 
Epigomphus.| 
Gomphus. 
Neogomphus. 
These two subgenera were originally united under Ophiogomphus by M. Se- 
lys. I retain them as separate in deference to his high authority, but I can 
perceive no distinguishing characters that are not rather of specific than of 
subgeneric value. To consider the characters laid down by Messrs. Selys and 
Hagen in detail:—Isi. The difference in the thoracic stripes. If species with the 
normal thoracic stripes subobsolete are to be placed on that account in a sepa¬ 
rate subgenus from those with the normal thoracic stripes distinct, surely those 
with the normal thoracic stripes entirely absent ought also to be placed in a 
separate subgenus. ISTow Mr. Selys himself refers to Erpetogomphus a species 
{boa) with the thorax immaculate; (Addit. Synops. Gomph. p. 11 ,) and I have 
described another one (rupinsulensis,) which also has the thorax immaculate. 
2nd. The different length of the legs. Calculating from M. Selys’ own measure¬ 
ments, in JErp. crotalinus the hind wing is 4.28 of the hind femur, while in 
Oph. colubrinus % and Oph. serpentinus % the hind wing is respectively 4.21 
and 4.20 of the hind femur—the difference in this respect between the two sub¬ 
genera being as small as it well could be. It is possible, however, that the 
tibiae in Ophiogomphus may be disproportionately elongated, so that the entire 
hind leg may be relatively to Erpetogomphus much longer, instead of being 
subequal as we should infer from the subequality of the hind femora. But even 
allowing that the legs of all known Erpetogomphus are short, and those of all 
known Ophiogomphus long, the enormous and yet very gradual difference in 
the length of the hind femur between the different species of the Subgenus 
