MAY FLIES AND MIDGES OP NEW YORK 59 



securely to the rock surface. The net winged midge B 1 e p h a r - 

 o c e r a is the commonest associate of this species in Coy Glen. 



This is another genus that has not hitherto been known east- 

 ward of the Rocky mountains. 



Rhithrogena elegantula Etn ? 



For the sake of illustrating a still more perfect development 

 of the ventral abdominal disk framed with gill lamellae, as well 

 as illustrating the variety of form in this group, I insert here a 

 figure and a brief description of a nymph from Twin Lakes, 

 Colorado, sent me for study by Mr Chauncey Juday, collected in 

 the summer of 1902 : 



The nymph. (P1.7, figs.4 and 5.) Length of full grown female 

 nymph, 10 mm.; male, 9 mm.; antennae and setae broken. Body 

 short, stout, flat, narrowly elliptical behind the dilated head; 

 head widest across the eyes, semicircular in outline, its thin 

 lateral margins naked; behind the widest portion the sides con- 

 verge with very great abruptness to the hind margin; antennae 

 short and stout and bare, the joinings of the segments becoming 

 oblique apically. Mouth parts as shown on figs.!2i, 13c and 14o. 



Prothorax three to four times as wide as long, produced at the 

 sides in an olbtuse projecting angle; legs rather short and nearly 

 bare, the femora moderately curved and flattened with a fringe 

 of rather stiff, very short bristles on the curving superior carina; 

 each of the claws with a basal lateral tooth (fig.lla?). 



Abdomen short and ovate; gill plates on segments 1-7 mem- 

 branous, white, obtuse, closely superposed at their broadly over- 

 lapping edges, bearing copious tufts of long, simple gill filaments 

 at their bases above. The anterior ends of the lamellae of the 1st 

 segment meet beneath the onetathorax, and the incurved tips of 

 those of the 7th segment meet beneath the slightly upcurved tip 

 of the abdomen. Setae in male 2, with a rudimentary middle one, 

 in female 3 well-developed, bare, the median paler than the others ; 

 extreme bases of setae (brown, like the general integument of the 

 body. 



EPHEMERINAE 



Since the publication of bulletin 47 I have made no new breed- 

 ings in this subfamily, but my friend Mr W. E. Howard of 

 Ottawa, 111., has reared and studied our Polymitarcys 

 a 1 b u s Say and has prepared at my request the following 



