MAY FLIES AND MIDGES OF NEW YORK 19 



this group. As is well known, tliere is with majflies one moult 

 during adult life. The nymph, transforming, leaves the water as 

 a subimago, and later moults again and becomes the imago. The 

 subimago stage lasts 'but a little while — ^but a few minutes with the 

 most ephemeral species, about a day with the majority of species, 

 two days Avith S i p h 1 u r u s alter n a t u s kept indoors — ^being 

 much more brief than is the jjeriod of transformation of even those 

 species that are most concerted in time of appearance on the wing. 

 It follows from this that when one finds subimagos flying, he can 

 go to the water whence they came and be rather sure of finding, 

 with proper searching, the full-grown nymphs. The subimagos 

 may be recognized by their generally duller coloration, and the 

 possession of fringes of hairs around the wing border (present in 

 the imago of C a e n i s only among our forms) . Grown nymphs 

 may be placed in any sort of a dish of water near a window out 

 of the direct sunlight to transform. The subimagos picked from 

 the window later may be put in paper bags and left to moult 

 again. All stages are best preserved directly in alcohol of about 

 80 per cent strength. 



Besides the material for this paper collected by myself and Mr 

 Betten at Ithaca N. Y. and Lake Forest 111., and that furnished 

 me from the State Museum collection by Dr Felt, I have received 

 material used herein from Professor T. D. A. Oockerell collected 

 at Pecos New Mexico, from the late Mr E. J. Weith, collected at 

 Elkhart Indiana,, from Mr Chauncey Juday, collected at Twin 

 Lakes Colorado, and from Mrs Mary Rogers Miller, collected at 

 Thousand Island Park N. Y., for all of which I return grateful 

 acknowledgment. 



For the use of the following keys a little more knowledge of 

 mayfly structure is likely to be required than the average text- 

 book of entomology affords. A knowledge of the names of the 

 parts of the body and legs of the typical insect will be assumed; 

 also, of the principal mouth parts and antennae. It should be 

 known that the male is readily distinguished from the female by 

 the possession of much larger comipound e\x^s, these always being 

 remote from each other in the female, and by the possession of a 

 pair of jointed appendages called forceps that project backward 

 from beneath the penultimate segment of the abdomen. The two 



