REV. A. E. EATON ON EECENT EPHEMERID,^ OR MAYFLIES. 249 



CiNYGMA PAR, sp. iiov. Plate LXV. 5 (genitalia). 



Imago '{dried), 6 . — Notum light pitcli-brown, sometimes approaching light luteo- 

 piceous anteriorly at the sides. Dorsum of the abdomen Vandyke-brown and opaque in 

 segments 8-10 ; the other segments for the most part are lighter and somewhat trans- 

 lucent, the dark colouring at their tips being shaded off anteriorly and encroached upon 

 by dirty-whitish subtransparent spaces, viz. : — a large space on each side of the back in 

 front, a narrow strip extending across from the one space to the other along the anterior 

 margin of the segment, and three longitudinal linear streaks proceeding from the base 

 nearly to the terminal border of the segment, of which the intermediate (coincident 

 with the course of the dorsal vessel) and the others are narrowly edged with dark 

 colouring : in the large subtransparent spaces referred to the trachea? are visible, and in 

 some lights appear slightly brownish ; the hinder angles of the pleurae are pale. Venter 

 in segments 3-7 translucent, Avith conspicuous nervous ganglia of a light warm sepia- 

 brown ; the hinder segments opaque, and of a very light brownish ochre. Setge light 

 warm sepia-brown. Legs in opaque view bistre-brown, the base of the fore femur and 

 the fore trochanter rather lighter, the insertion of the fore tarsus slightly darker : in 

 transmitted light their predominant colour is brown-amber or golden brown. AVings 

 vitreous, tinted with light bistre-grey throughout, but with a stronger tint than else- 

 where in the j^terostigmatic region of the fore Aving and at the wing-roots : neuration 

 in opaque view bistre-brown, changing in transmitted light to raw-umber brown : the cross 

 veinlets of the pterostigmatic space in the fore wing are mostly simple and seldom 

 anastomo seat all, and then only irregularly and very sjiarsely. Length of body, <S 8 ; 

 wing 9-10 ; sette, 6 im. 18-20 mm. 



Hah. Arizona (M'^Lach. Mus.). 



CiNYGMA MIMUS, sp. UOV. 



Imago {dried), 6 . — Very similar in aspect to the European Rhithrogena semicoloruta. 

 Notum either liglit raw-umber or light chestnut-brown. Abdomen discoloured : in 

 opaque view segments 7-10 are in some specimens of a light broAvnish colour approaching 

 broAvn-ochre, and the remaining segments of a light purplish broAvn ; but in other 

 specimens the prevailing colour is more nearly madder-brown : segments 2-7 are each of 

 them colourless and transparent at the extreme base, and the colourless spaces, narroAV 

 in the middle, are enlarged a little by the pleurae, presenting thereabouts a small rounded 

 expansion on each side bounded posteriorly by the anterior trachea? of the segment : the 

 arrangement of the ventral colouring resembles that of the dorsum. Seta? light raw- 

 umber brown. Legs light yellowish brown, approaching raAV-umber or dull bronze- 

 broAvn in some lights, with the insertion of the fore tarsus and the ungues of that foot 

 light pitch-brown, and the hinder tibia? and tarsi rather lighter and yellower than the 

 femora ; in transmitted light the femora and fore tibiae become light brownish amber, 

 and the remainder yelloAvish amber. Wings vitreous with raw-umber brown neuration 

 varying in intensity Avith change of light : but the subcosta and radius to the middle, 

 md the basal extremities of the hinder longitudinal nervm-es of the fore wing, and the 



