46 NEW YORK STATE MUSEUM 



operculate^ overlapping the next behind it hardly more than that 

 one overlaps its successor. Setae slender, pale, ringed with dark 

 brown at base, thinly hairy except at base (Plate 10, flg.7). 



Ephemerella sp? 



Professor T. D. A. Cockerell has sent me from Pecos, N. Mex., 

 a single n.ymph of so remarkable form ( Plate 9, fig.2) . I desire to 

 make it known herewith. Its affinities are obviously with 

 Ephemerella ex crucians, and it differs from all the 

 " allies of Ephemerella" figured by Eaton from western 

 North America. Therefore I briefly characterize it here and 

 present a figure made from a photograph of the single known 

 immature specimen. 



Body excessively flat and thin, about twice as long as wide, 

 widest across the middle of the abdomen. Head short and much 

 narrower than the protliorax; eyes and ocelli dorsal, remote; 

 antennae short, bare, about as long as the head is wide, composed 

 of only about twelve segments, of which the basal one is as usual 

 longest and thickest. 



All lateral margins very hair^-. Prothorax half as long as 

 wide, straight on front and sides with rather acute front angles, 

 somewhat widened posteriorly. Legs short; femora flattened, 

 widest before the middle and fringed on both margins. 



Abdomen short, about as wide as long, excessively flat, with 

 huge, serrate lateral spines on segments 2-9, increasing in breadth 

 posteriorly, but longest on the middle segments, all strongly 

 curved posteriorly. Segments slightly incre^ising in length suc- 

 cessively to the 8th, 9 much longer, 10 only about one fifth as 

 long as 9, but slightly ^jroduced on the dorsal side. Gills cov- 

 ered by an oblong opercular laimella attached at the apex of 

 segment 4. Of the underlying gills T have made no examination, 

 not wishing to injure the unique s{)ecrnien. Setae 8, closely paral- 

 lel at base, broken in the specimen. Coloration very obscure, the 

 animal being apparently covered in life by adherent silt, but there 

 is a trace of a brownish ring on the middle of each tibia and 

 another on each tarsus. 



Pecos, New Mexico, July or August 1903. 



Professor Cockerell sent rae from Pecos also a fine pair of 

 imagos and these may represent the same si>ecies as the nymph 

 above described. I should have felt inclined to refer these to 

 Ephemerella inermis Eaton but for the conspicuously 

 bifid prolongation of the 9th abdominal sternum in the female; 



