L6 THE [MMATURE STATE OF THE ODONATA. 



ventral posterior edge of segmenl 9 fringed with hair; genitals slightly 

 marked ; ventral bags on base of segment 6 ; a suture near the ventral side- 

 margins of segments 3 to 9. Legs very long, thin, cylindrical ; hind legs 

 wide apart at the base, a little more so than middle legs ; tore legs nearer 

 together; between middle legs are two elevated ridges, for receiving the base 

 of the mask ; between the bind legs is a rounded protuberance ; hind legs a 

 little longer than middle legs; fore legs shorter; femur of hind legs reaching 

 segment 9 ; tibia a little shorter ; tarsus half as long, first joint very short, 

 second and third long, equal ; claws long, sharp, incurved, not divided at tip. 



Thorax and abdomen above much variegated with gray and white, form- 

 ing a series of ill defined large pale-colored spots; femur with three blackish 

 bands, tibia mottled with gray. 



1 have seen a large number of very young nymphae, 9 mm. long, and full- 

 grown ones. As the very young ones and those about full grown were 

 collected together in fall and midwinter (December), they need probably 

 two years for full development. They transform in the imago from May to 

 June, so far as is known. 



The principal characters which separate the previous stages of M. trans- 

 versa from those of M. Illinoiensis are a narrower, saddle-shaped head, the 

 abdomen truncate at tip, the want of any indication of a dorsal hook on the 

 last segment, and longer lateral spines of ninth segment. The body is less 

 flat and more roof-shaped before the young ones undergo the first change 

 of the skin. These differences of the previous stage of M. transversa justify, 

 perhaps, the retention of the genus Didymops of Rambur for this species. 



3. MACROMIA ILLINOIENSIS. (Supposition.) 



Plate I. Fig. 2. Plate II. Fig. 1. 



Imago. Macromia Illinoiensis Walsh, Proc. Acad. Philad., 1862, p. 397. Selys, Synops. 



Cordul., p. 109, no. 69. 



Nympha dry, and nympha skin, from Massachusetts ; three nymphae, one 

 full-grown, locality not known, and one skin in alcohol, from Dendridge 

 Junction, Tenn. ; two nympha skins from Detroit, Mich., from H. G. Hub- 

 bard. Mackinaw Creek, Woodford Co., 111., August 20, 1879 ; S. 111., a large 

 female nympha, two from Union Co., 111., July 17, 1877; Peoria, 111., Octo- 

 ber, 1878; — all from Prof. S. A. Forbes. 



Length, 19 to 30 mm.; breadth, 9 to 13 mm. 



