1863.] 
255 
when it readies half-way to the notuin : under and rather behind the front 
wing, at the upper hind corner of the anterior pleural segment, a large, ill- 
defi'ned, roundish, yellowish spot, in the same line with the yellow stripe. Ab¬ 
domen long, robust, inflated at base, gradually contracted to the tip, with the 
hind edge of joints 2—5 narrowly yellow; venter brown. Abdominal appendages 
tipped with blackish, pilose. Viewed from above they are cylindrical, slightly 
contracted towards their base, slightly bent outwards at i the way to their tips. 
in Erpetogomphus 9 ‘* 8—10 diminish successively in length,” how much not 
being specified. {Mon. Gomph. p. 401.) In my Erp. rupinsulensis %, on the 
most careful measurement, 8—10 are respectively 3J, 2J and 2 millimetres long, 
thus making joint 9 three-eighths as long again as 10 in % Erpetogomphus, 
whereas, according to M. Selys, joint 9 in Erpetogomphus is equal to 10. On 
the other hand, although M. Selys says that in Ophiogomphus ^dO is half as 
long as 9,” yet on measuring the of the two species of Ophiogomphus fig¬ 
ured by Dr. Hagen, we find joints 9 and 10 to average respectively 7i and 4^ 
millimetres. The difference between these proportions and those found in my 
^ Erpetogomphus is scarcely sufficient to afford a character of much subgene¬ 
ric importance. If joint 9 in % Ophiogomphus was proportioned to 10 as it is 
in my Erpetogomphus, it would measure a small fraction over 5| instead of 
1\ millimetres ; and if joint 9 in my Erpetogomphus was proportioned to 10 as 
it is in % Ophiogomphus, it would measure a small fraction over 3-1 instead of 
2f millimetres. Such differences are practically worthless, as subgeneric cha¬ 
racters. 
After the above was in the hands of the printer, I received from Mr. A. S. 
Packard, jun., of the State of Maine, the following brief description of the 9 of 
what is evidently an undescribed species of Ophiogomphus. Mr. Uhler had 
previously informed me that he had received from the same source an unde¬ 
scribed Ophiogom 2 :)hus, which, so far as he recollected, was %. It will be no¬ 
ticed that it agrees with Ophiogomphus Selys, in the armature of 9 occiput, and 
with Erj>etogomphus Selys, in the thorax being chiefly green and in the vesicle 
of the vertex being divided into two tubercles. In the “ Additions and Correc¬ 
tions” to the Monographie, however, M. Selys himself modifies the characters 
of Erpetogomphus by saying that‘‘the six stripes of the front of the thorax 
may be pretty wide and blackish,” (p. 431.) On the other hand the hind wing 
in 9 of this sj)ecies is 5.71 of the hind femur, according to Mr. Packard, while, ac¬ 
cording to the Monographie in Ophiogomphus serpentinus 9 it is 3.88 of the hind 
femur. In Erpetogomphus crotalinus 9 > according to the measurements of the 
Monographie, it is 4.14, in E. designatus^ 5.58, and in E. compositus^ 6,00, or in 
the average of the three species 5.24, thus making the average hind femur of 9 
Erpetogomphus considerable longer, instead of shorter, than it is in this now 
species of OphiogomjDhus. These additional facts prove, I think, conclusively 
that the subgenus Erpetogomphus must be suppressed. 
Ophiogomphus mainensis Packard, n. sp. “ 9 Glreeu varied wit4i brown. 
Front of the head green, pale and whitish in the neighborhood of the mouth. 
Vesicle of the vertex divided by a medial impressed line into two low tubercles, 
