MAY FLTES AND MIDGES OF NEW YORK 



53 



The nymplis in this subfamily are recognizable at a glance by 

 their dorsally placed e^-es, with the lateral flaring margins of the 

 sides of the head projecting beneath them. They are all strongly 

 depressed also, and have lateral pectinations to the tarsal claws 

 (fig.ll), aiding them doubtless in clinging to their supporting 

 surfaces washed by currents of streams or waves of shores. 

 Further than this, however, there is very great diversity among 

 them, and E c d y ui r u s , Iron and Rhithrogena fur- 

 nish a most interesting illustrartion of a special adaptation to 

 life in torrents. In E c d y u r u s (pl.lO, flg.3) the gill lamellae 



P ^Fig-. 14 Maxillae of nymphs of Heptageninae ; m, of Iron sp ? from Coy Glen, 

 Ithaca;n,of Heptagenia interpunctata Say; o, of Rhithrogena elegan- 

 t u 1 a Etn. V ; p, of E c d y u r u s m a c u 1 i p e n n i s Walsh 



are all divergent and the gill filaments are beneath their bases. 

 In Iron (pi. 10, figs. 6 and 7) and in Rhithrogena (pi. 10, 

 fig.l and 5) the abdomen is more limpet-shaped, and the gill lamel- 

 lae form a closely overlapping series whose outer border fits the 

 supporting surface. to which the nymph clings as closely as do also 

 the flaring lateral and front marginsi of the head; but this is not 

 all, the gills have migrated outward and now lie upon the bases 

 of the lamellae, exposed on the outside to the stream of water 

 which now dashes over, but does not flow beneath the lamellae. 

 Furthermore, by the enlargement and approximation beneath 

 the thorax of the foremost lamellae and by the depression and 

 inward curvature beneath the tip of the abdomen of the hindr 

 moist of them, there is formed beneath the abdomen a disk for 



