382 PROCEEDINGS OF THE ACADEMY OF 



verse ; and that in Agrionina, even in the same sex, and at the same stage of 

 maturity, and while the insect is still alive, a very great variation of color is 

 often observable. For example, many adult 9 of Agr. Ramburii occur, that 

 are orange instead of blue. In Agrionina the dark markings also are often 

 variable in the same sex, and differ most wonderfully in the two sexes. On the 

 contrary, the coloring of the legs, as is generally the case in most families of 

 Insecta, is in Agrionina, except in very immature individuals, remarkably con- 

 stant in the same species, does not, so far as my experience extends, vary in the 

 sexes, and varies very considerably in different species, while on the other hand 

 it does not fade or change materially in drying. It fulfils, therefore, if this be 

 correct, all the conditions of a good specific character. Hence, it ha3 occurred 

 to me. that a little more precision might be advantageously introduced, in this 

 tribe, into the nomenclature of the colorization of the leg, and more particu- 

 larly the femur. Just as in Gomphina, on each side of the dorsum of the thorax 

 there exist three normal dark stripes -the dorsal, the antehumeral and the 

 humeral each of which has its locus definitely ascertained; so in the femur of 

 Agrionina there exist three normal dark vittae, the locus of which is susceptible 

 of being accurately determined. That this is so, any one may convince himself 

 by comparing Lestes unguiculala, or some other species which has all the three 

 normal femoral vittae coexisting, with other species of Lestes or Agrion which 

 have a smaller number of femoral vittae. He will find that the difference be- 

 tween them is merely that one or more vittae are obsolete, and that those vittae 

 which are not obsolete retain the same invariable locus. 



Supposing the leg, with the knee slightly bent, to be extended horizontally 

 at right angles to the body, and in such a position that the tibia and femur 

 shall both lie in the same vertical plane, the back of the insect being of course 

 supposed to be uppermost ; I call that vitta whose locus lies underneath, and 

 does not extend beyond the two lateral rows of spines, which are always in 

 Agrionina present on the inferior surface, 'the inferior vitta." This has 

 generally by authors been called " the interior." The vitta whose locus lies 

 above, with its two edges equi-distant from the two rows of spines beneath, I 

 call "the superior vitta." And the vitta, whose locus is on the anterior side 

 of the femur, betwixt the "inferior" and the "superior," I call ' ' the anterior 

 vitta." Strictly speaking, these are, I believe, all the vittae which exist on 

 the odonatous femur ; and there is no such thing in Nature as a posterior black 

 vitta on the femora of an Odonate. But just as, for convenience sake, M. de 

 Selys sometimes considers the ground-color of the thorax of Gompkus to be 

 black, and enumerates its yellow stripes,* which of course changes the locus of 

 every stripe, the so-called yellow stripes occupying the intervals between the 

 normal black ones ; so it is sometimes convenient, when the inferior, anterior, 

 and superior vittae are all confluent, leaving only the posterior part of the 

 femur pale, to consider the femur as being black with a posterior pale vitta. 

 Dr. Hagen has remarked, that the true ground-color of the thorax in Gompkus 

 is pale, because some species occur with the thorax all pale, and none with the 

 thorax all black ; and for this reason he seems to object to M. de Selys's 

 nomenclature. There is a wide difference, however, between these two cases. 

 The imaginary pale vittae on the thorax of Gomphus have a different locus from 

 the normal black vittre ; while the imaginary posterior pale vitta on the femur 

 of Agrion has precisely the same locus as a normal posterior dark vitta would 

 have, supposing such a vitta to be possible. 



The "anterior" and "superior" vittae are confounded together by authors 

 under the name of "exterior;" and sometimes, when there is a pale "pos- 

 terior" vitta, the femur is said to be " pale below" thus giving rise to a great 

 deal of confusion between the true "inferior" and the "posterior" vitta. In 

 many species the inferior and the anterior are confluent ; and it is very fre- 



* See the svnoptical tables opposite page 14 of the "Monogr. des Go mphmes." 



[Sept. 



