270 
[October 
(jraphie calls this supernumerary suture the first pleural suture, that 
dividing the mesothorax from the metathorax the second or median 
suture, and sometimes “the suture under the wings,” and that behind 
the metathoracic episternum the third or sometimes the ventral suture. 
(^Mon. Galopt. p. 11.) Considering this false or supernumerary suture 
as a true one, it is a remarkable fact that in Gromphus the locus of each 
dark pleural stripe is always in or on a suture^ and in Hetaerina between 
two sutures. But as if to show how Nature never proceeds by sudden 
leaps, there exists in many Hetasrina, in addition to the normal dark 
stripes between the sutures, a short black line at the upper part of 
the pleura in one or two of the sutures. 
Strictly speaking, there are typically three., not two, dark pleural 
stripes in Gromphus. For example, in several Onychogomphus (groups 
geometricAis and grammicus and certain species of the group cognatus,) 
in Ceratogomphus, and in one single species of Gomphus, G. paroulus, 
there is said to exist a third dark pleural stripe “ on the posterior bor¬ 
der” of the metathorax or “ on the third suture.” {Mon. Gomph. pp. 
16, 18, 19, 66, 77, 158.) In Gomphus melsenops, G. minutus and G. 
occipitalis the Monographic especially notices the absence of this third 
pleural stripe, (pp. 129, 156, 166.) Just as in G. kurilis the first 
dark pleural stripe is obsolete, and in G. fraternus and a few other 
species the second dark pleural stripe is almost always obsolete, so in 
all 37 Gomphus, except parvuhis, and in many other subgenera of the 
great genus Gomphus, this third pleural stripe is obsolete. In Platy- 
gomphus the pleural dark stripes are all three of them obsolete. In 
Erpetogomplms boa Selys, and E. rupinsulensis Walsh, not only are 
all the three typical dark pleural stripes obsolete, but also the three 
typical dark stripes on each side of what is called the dorsum of 
the thorax. In the other species of Erpetogomphus these last are 
only subobsolete. The important point to observe is, that wherever 
any of these dark thoracic stripes exist, their locus is definitely fixed.* 
So that if we believe that each species of, e. g., the 37 described species 
of Hetaerina and of the 86 described species of Gomphus was sepa¬ 
rately created, and not derived by hereditary descent from some one 
- Dr. Hagen well observes of the extra-American Legion Lindenia (Goni- 
phina) that “ by fixing the primitive designs [of the thorax], we may always 
derive from them the special variations.” {Mon. Gomph. p. 251.) 
