Vol. xxvii] ENTOMOLOGICAL NEWS. 327 
which is an appendange of the ventral side of abdominal seg- 
ment two consists usually of three segments and two, usually 
unchitinized folds. Segment 1 is the basal or proximal, slen- 
der, heavily chitinized shaft. Segment 2 is the moderately 
chitinized median segment, while segment 3 is the apical or 
distal segment which folds 
forward on the median Oe.2. S eg.d. 
segment and is usually un- 
chitinized. The median 
segment ordinarily carries 
across its ventral surface a 
fleshy ridge or fold, the 
inner fold, and across its 
posterior end the terminal 
fold. This latter is prob- 
ably erectile in many spe- Diagram showing the parts usually found 
ies) Either or both fleshy i ‘R*2%EoPterous pens. 
folds may be lacking and in the Legion Lestes segment 3 is 
much reduced. The differences between penes are usually in 
the shape of the distal or third segment. 
I have introduced this present series of papers with this 
one on Acanthagrion to have it appear in conjunction with a 
paper on some species of the same genus by Mr. Williamson. 
The study of the penes in this group at once cleared up the 
hitherto obscure relations of the various forms which had 
variously been termed varieties and subspecies. Those that 
have been studied are, as far as the penis is concerned, good 
species. Mr. Williamson and I were both much surprised 
when we found the great structural differences existing in the 
penes of the so-called “subspecies” (ablutum, ascendens, mi- 
narum'), of gracile. ‘The penes of the thirteen species of 
Acanthagrion I have been able to examine vary more among 
themselves in form than those of any similar group of closely 
related species of Zygoptera. If I had seen the penes only, I 
Internal fold. 
Seg.l. 
Terminal fold. 
4The minarum referred to by Mr. Kennedy is the species described 
by me (anted, p. 314) as kennedui. It was determined independently by 
Dr. Calvert and myself as minarum, but is probably not the minarum 
of de Selys—E. B. WILLIAMSON. 
