204 ENTOMOLOGICAL NEWS. [July, ’12 
The sixth (instead of the fifth) antenodal is thicker on the left front 
wing of the female. 
The abdomen of the male is widest at segment 9. 
Erpetogomphus tristani 6 falls under rubric AA of the key 
to the species of this genus (Biol. Centr.-Amer. Neur., p. 160) 
so far as the superior appendages of the male are concerned, 
but the face has distinct dark markings. It is also allied to E. 
ophibolus of rubric A in possessing a superior tooth on the 
same appendages. In possessing both a superior and an infer- 
ior tooth, both well-developed, and such a strongly recurved in- 
ferior appendage, it differs from all other described species 
of Erpetogomphus. 
The female tristani falls under rubric BBB of the same key 
1. c., p. 162) and in its occipital characters and brown ante- 
humeral (+ humeral) stripe comes nearer to diadophis than to 
designatus, but differs from these and all other known species 
by the peculiar structure of the vertex, which deserves fuller 
mention. 
Mr. Williamson (1899) first pointed out that in the Odonata 
Anisoptera, in pairing, the inferior appendage of the male rests 
on the top of the head of the female and the superior appen- 
dages of the male on the rear of the head of the female. He 
was able (1906) to make positive observations to this effect in 
the genus Gomphus, among others. Calvert (1906), in confirma- 
tion, figured the two sexes of Aeshna constricta |[=umbrosa, 
E. M. Walker] in this position. There is no reason to think 
that the mating position in Erpetogomphus is different. In the 
above description and in the figures (Figs. 3, 4) of the vertex 
of the head of £&. tristani female, mention is made of a deep 
median longitudinal groove (g), and of the great reduction of 
the dorsal surface of the occiput. On placing the head of the 
female and the hind end of the male abdomen side by side in 
the same field of the microscope, it is evident that the recurved 
terminal part of the inferior appendage of the male (Fig. 8) 
is sufficiently narrow transversely to be received into the me- 
dian vertical groove of the female. It seems inevitable that 
the inferior appendage should fit into this groove when pair- 
ing takes place. It is also likely that the ventral tooth of each 
