1^6 PSYCHE [August 



segments feebly developed in the younger specimens, the ratio of length of segments from 

 the base outward being i : 1.3 : 2 : 1.5 : i : .8 : .5. Hind angles of the head prominent, 

 obtusely rounded, scurfy pubescent, with a wide but shallow notch on the hind margin 

 between them. Labium short, the hinge reaching posteriorly only so far as the middle of 

 the prothorax. Mentum with a very prominent, entire median lobe, and with no mental 

 setae. Lateral lobes short and stout, each with a strong arcuate movable hook and a single 

 weak raptorial seta just before base of hook. The end hook is cut otf from the inner margin 

 by a feebly developed notch and above it on the end of the lateral lobe is a second similar 

 but somewhat smaller hook, that is denticulate on its external margin. 



Prothorax short, widened and thickened toward its rear margin. Legs short, stout, 

 thinly fringed with hairs. Wing cases (in the oldest of these immature specimens) reaching 

 only the middle of the 2d abdominal segment. 



Abdomen cylindric, the segments of nearly equal length, except at ends where somewhat 

 shorter, the loth segment excised on mid-dorsal margin. Gills oblong, widest just beyond 

 the middle, suddenly contracted to both ends, the superior a little shorter than the laterals, 

 all subinflated in the basal half, and with very prominent lateral carinae along the axis. 



Color pattern unusually well developed. General color greenish brown, paler below and 

 on sutures : a mid-dorsal row of pale triangles on the abdominal segments, one on each 

 segment, and a pale line each side, and a row of oblique pale streaks in the darker color of 

 the side margin. There is a blackish lateral band extending from the rear of the eyes along 

 the sides of the head and prothorax. All the femora bear two distinct broad rings of blackish 

 brown, the distal one being the more prominent, the gills are blackish, white tipped, and 

 each shows an imperfect pale subapical transverse band starting inward from the opposite 

 margins and of different extent in different specimens. The depth of color varies greatly 

 Avith remoteness from time of moulting, but the general pattern is quite apparent in all but 

 the most recently moulted. • 



Material more recently collected from the same place on March 21st, 1903, 

 includes some larger specimens measuring in length of body 16 mm., having wing 

 cases reaching the middle of the 3d abdominal segment. 



This nymph is at once distinguished from our other known agrionine nymphs 

 by a very primitive character : the possession of triquetral gills, having swollen 

 base and thick lateral carinae. Of all the nymphs of Odonata hitherto made known 

 they are most like the fossil nymphs of the genus Samarura described by Brauer, 

 Redtenbacher, and Ganglbauer in the Memoirs of the Imperial Academy of St. 

 Petersburgh, vol. 36, 1888, from the Jura formation of East Siberia. The gills 

 are very similar. Nymphs of Hyponeura agree closely with those of the genus 

 Argia, differing chiefly by their much greater size, shorter labium, absence of well 

 developed raptorial setae, and thicker gills. The species of Argia from streamlets 

 of warm water above mentioned has triquetral gills, possessing strong lateral carinae, 

 but they are thinner and more pointed than the gills of Hyponeura nymphs. In 

 Argia pntrida Hagen, which clings to the rocks in rapid streams or on wave beaten 

 shores, there are feebly developed lateral carinae at the base; but the other species 



