246 REV. A. E. EATOX ON RECENT EPHEMERID^ OR MAYFLIES. 



light colour, and the dark colouring of the terminal margin of each of the intermediate 

 segments does not enter their hinder lateral angles, but a short bistre-brown streak runs 

 in a curve from the said margin to the scar of the nymphal tracheal branchia on each 

 side of every such segment very near the said angles. Venter of a light colour, trans- 

 lucent, apparently showing the light brownish ganglionic cords, and perhaps a small 

 whitish spot on each side of them in each of the 2nd to 7th segments. Porceps-basis very 

 salient in the middle behind. Setae light warm sepia-brown. Femora and anterior 

 tibia in opaque vieio translucent raw umber [in some lights rather yellower], the former 

 each with a rounded black spot in the middle, and the latter bistre-brown at the insertion 

 of the tarsus ; fore tarsus dull light yellowish brown ; hinder tibiae and tarsi light 

 yellowish brown or brownish yellow, with [in some positions of the specimens only] the 

 terminal joint and the distal edges of the other tarsal joints light brownish. Wings 

 vitreous ; neuration of the fore-wing in opaque view light pitch-brown, but the great 

 cross vein, the baseward extremity of the subcosta, and those of the nervures posterior to 

 it are somewhat deficient in colour ; the neuration of the hind wing also, as a whole, is of 

 a similarly pale colour ; in transmitted light the stronger nervures of the fore wing 

 become light brownish amber ; pterostigmatic cross veinlets simple. Length of body 

 9-10 ; wing 11 ; setse, 6 im. about 26-33 mm. 



Hab. Colorado (M'Lach. Mus.) ; Manitou, Col. (Morrison, in Mus. Comp. Zool. 

 Cambridge, Mass.). 



Iron nitidus, sp. nov. Plate LXV. 3 (genitalia). 



Imago {dried). — s . Notum light brown-ochre. Abdomen above and beneath in 

 segments 2-7 very light bistre-brown (or in small examples very light yellowish 

 ochre) somewhat translucent, with the joinings opaque, the dark colouring filling the 

 hinder lateral angles of the segments ; segments 8-10 light brown ochre, sometimes with 

 the dorsal joinings light brown. Porceps-Hmbs light bistre. Setse in some lights 

 whitish yellow, tinged towards the roots with brownish ; in other lights their predominant 

 colour is light yellowish brown. Pore femur and tibia in opaque view light raw-umber 

 brown, the latter bistre-brown at the insertion of the tarsus ; foi'e tarsus whitish brown- 

 ochre, with the joinings, the terminal joint and ungues slightly brownish ; in transmitted 

 light their predominant colours change to brownish amber and whitish amber respec- 

 tively. Hinder legs in opaque view very pale yellowish, approaching whitish yeUow- 

 ochre, with the extreme bases of the tibiae, the tarsal joinings, terminal joints, and 

 ungues warm sepia-brown. Wings vitreous, strongly iridescent; the pterostigmatic 

 region of the fore wing tinted with extremely light raw-umber ; the remainder of the 

 marginal and submarginal areas more faintly so tinted, and the other part of the wing 

 almost imperceptibly so ; neuration raw-u.mber brown ; pterostigmatic cross veinlets, 

 almost without exception, simple. 



Variation. — In opaque view the 6 fore tibia is lighter than the femur, and the tarsus 

 is uniformly light bistre-brown : in transmitted light the tibia and tarsus are almost 

 concolorous. 



