467 



labial palpi. The caudal gills are dark, with a light transverse band 

 about the middle of their length. The caudo-lateral margins of the 

 head are elevated to form a short, sharp tubercle. The nymph of but 

 one species has been available, and a study of this, together with a 

 comparison with Hetaerina, has afforded possible generic characters. 

 The adults are uniform in color, usually dark metallic green or 

 blue, and black, and the wings are broad, with a large number of 

 cross-veins, the basilar space, however, being free from them. The 

 legs are provided with a double row of ventral setae which are usually 

 several times longer than the spaces between their bases. 



Key to Species 



a. Intersternum metallic green ; wings of male smoky only on the apical 

 third; female with a sharp spine on the dorso-apical margin of the 



tenth abdominal segment ; latero- ventral margins of thorax pale 



aequabile. 



aa. Intersternum entirely black ; wings of male wholly dark ; female with 

 only a short blunt projection on the dorso-apical margin of segment 

 ten ; latero-ventral margins of thorax dark maculatum. 



Agrion aequabile (Say) 



Nymph. — The nymph of aequabile has not been available for 

 study, but this species and its variety yakiuia have been described by 

 Needham ('03:223,224) and Kennedy ('15:338). It seems to be 

 nearly identical with maculatum. The length of the basal segment of 

 the antenna is used by Needham for its separation from maculatum, 

 but this character can not be used for the separation of the variety 

 yakima. The length is somewhat greater and the gills somewhat 

 longer than those of maculatum, but this character also is of doubtful 

 importance, and further study of the two species should be made to 

 determine the essential differences. 



Adult; Male. — Color, metallic green and blue. 



Head : mouth-parts black, median lobe of the labium triangular 

 in outline, basal segment of the palpus very broad, distal segment 

 small, cylindrical, longer than the fixed hook of the first; palpiger 

 about one-third the length of the first segment ; antennae entirely 

 black ; clypeus and labrum black ; the front and genae metallic green 

 and thinly clothed with dark hairs. 



Thorax metallic green, black and green below ; pronotum with 

 the caudal margin entire, the caudal lobe convex and projecting caudo- 

 dorsad ; proepimeron distinct ; cephalic portion of the prescutum large, 



