MAY FI.IKS AM> MIIMIKS OK NK\V YORK 33 



lobe. Along the sides of the abdomen is an interrupted line of 

 black dashes on the lateral margin and there is a minute black- 

 dot .above the anterior end of each dash on either side of each 

 segment. Setae white, slightly tinged with yellowish on basal 

 segments, but not ringed. Forceps (pi. (5, fig.l ) long and 

 arcuate, the basal segment of each limb feebly differentiated; 

 coloration pale yellowish white, slightly infuscated in the middle. 

 $ imago. (Plate .">, fig.l ). Head above whitish or very pale lute- 

 ous ; ocelli ringed with black; a black spot beneath each eye and 

 another at its hind angle above upon a minute triangular back- 

 ward prominence of the occipital margin. Thorax tawny yellowish 

 brown above, the hind margins of the tergal sclerites narrowly 

 margined with blackish brown; venter deeper brown. Wings and 

 legs colored as in the male. Abdomen brownish rufescent, less 

 rufous than in the male, but with the apical lateral margins more 

 distinctly lineate with blackish brown. Segment 10 pale, pro- 

 duced .above into a posterior rounded loibe. Segment 9 produced 

 below in a long acutely bifid lamina, decurved at the apex, and 

 surpassing the level of the tip of the superior lobe on segment 10. 



A noteworthy feature of both subimago and imago, hitherto ap- 

 parently unnoticed in any mayfly, is the persistence of the maxil- 

 lary and coxal gill tufts of the nymph. These are present as 

 conspicuous blackish tufts on the inner sides of the front coxae 

 and at the sides of the atrophied maxillae. They are most con- 

 spicuous (probably because less dessicated) in the subimago, but 

 the constituent filaments, filled with black pigment, are easily 

 recognized in either. 



The nymph. ( Plate r>. figs. 3 and 4) . Length of full grown female 

 13 mm., antenna 4 mm. and seta 7 mm. additional. 



Body rather stout, thorax slightly compressed, abdomen 

 strongly depressed and upcurved posteriorly, its sides parallel as 

 far as the seventh segment, and distinctly wider than head and 

 thorax, then tapering to the base of the stout setae. Integument 

 strongly chitinized. 



Head short Avith vertical face, evenly contoured above, covered 

 at the sides by the low, broad, well-rounded eyes. Middle ocellus 

 directlv in front but the other two visible from a.bove. A median 

 frontal vertical carina below the middle ocellus ends in a stout, 

 sharp downwardly directed triangular spine. Antenna (Plate 0. 

 fig.O) stout, naked, basal segment stouter and paler, the shorter 

 segments immediately succeeding brownish, the succeeding seg- 

 ments again pale to the tip, Mouth parts unusually hairy, the 



