68 NEUROPTERA. 
Structural features must play a large part in specific identifications of Argia, not 
only because of their intrinsic value * but also because of the fading of colours after 
death; moreover, some species differing but slightly in coloration possess dissimilar 
structural characters (e. g. A. jfissa, A. deami, A. tarascana). On account of loss of 
colour, many types of de Selys and of Hagen are now unrecognizable except by the 
terminal abdominal appendages of the males and the mesostigmal lamine and 
mesepisternal tubercles of the females. 
The mesostigmal lamine are the “thoracic processes” or “ laminated processes of 
the thorax” of Hagen (1861) and the “lames du devant du thorax,” ‘‘ lames antérieures 
(ou elevées) du thorax” of de Selys?. I have called them mesostigmal lamine as more 
accurately defining their position, since each lamina is a prolongation posterior and 
superior to the mesostigma, or spiracle situated in the anterior part of the mesothorax 
(see Tab. IV. fig. 1). | 
To the best of my knowledge, the mesepisternal tubercles of the females have not 
been previously noticed in the literature of Argia. When present, they are two in 
number (right and left), one near the lower end of each mesepisternum to the outer 
side of the corresponding mesostigmal lamina. They are well developed in J. translata 
and A. tezpi (see Tab. IV. figg. 18,19), are present in A. masta, A. cuprea, A. harknessi, 
A. variabilis, A. vivida and its variety plana, reduced in size in A. ulmeca, A. deami, 
and A. extranea, and very small or absent in A. percellulata, A. sedula, A. pulla, 
A. oculata, A. popoluca, A. indicatriz, A. cupraurea, A. enea, A. difficilis, A. tonto, 
A. lacrymans, A. jfissa, A. tarascana, A. immunda, A. violacea and var. pallens, 
A. agrioides and var. nahuana, A. fumipennis, A. tibialis, and A. apicalis. 
The mesostigmal lamine and mesepisternal tubercles are female sexual characters, 
but whether they are employed in coition, as places of attachment for the male 
abdominal appendages, or not, is unknown. 
The shape of the male appendages and of the female mesostigmal lamine is 
mostly so difficult of accurate description that I have relied entirely upon figures 
(Tab. 1V.) to display it. 
As regards the descriptions given below of the colours of Argia, it is to be noted 
that the width of a single pale (blue, violet, &c.) antehumeral stripe (¢. ¢. on one side 
of the body) is compared with that of the entire dark (black, brown, &c.) mid-dorsal 
stripe (¢. e. on both sides of the mid-dorsal carina). It therefore follows that where 
the width of “the pale antehumeral stripe” is more than one-half that of the dark 
mid-dorsal, the predominant colour of the thoracic dorsum is pale. A pale ante- 
humeral stripe /ess than half as wide as the dark mid-dorsal means a predominantly 
dark thoracic dorsum. ‘The humeral stripe, when present, is dark-coloured and is 
sometimes described as ‘forked above,” meaning thereby that a dark mesepimeral 
* Selys has made a similar statement *, p. 381. 
