EEV. A. E. EATON ON RECENT EPHEMERID.E OR MAYFLIES. 257 



Naturk. Zwickau, 1877, p. 89 (1878) ; Palmuu, Paar. Ausf.-Gaiige d. Gcschl. Org. b. Insect. S. 44 & 52, 

 taf. ii. 30 (1884) [detail & anatom.] .— /f. semiiiticta, Mcyer-Diir, Bull. Soc. Eut. Suisse, iv. 312 

 (1874). 



Rhithrogtma [type] semicolorata, ! Etn., Ent. Mo. Mag. xviii. 23 (1881); nee Rh. semithida, ! id., in 

 the writing of PI. xxiv. 43 a of this work. 



Subimago {living).— Fovc wings very light grey ; hind wings paler. Legs greenish-, or 

 brownish-grey, with a small elongated spot in the middle of the femur, and with the 

 tarsus brown-Llack or grecnish-hlack. Setae very pale grey, s . Oculi dark olivaceous, 

 crossed by a transverse black line. {Dried.)— Fovg wings very light brownish-grey; 

 hind wings dull greyish white : femoral spots often indistinct or lost. 



Imago {living), J .—Genital stimuli narrowly ligulate, closely appressed to the lobes 

 of the penis, and acutely bi- or tri-deuticulate at the tips. Eyes intense raw-umber or 

 olive-brown above, and either black or pitch-brown below, and sometimes with a 

 bluish grey or greenish grey edging to this darker surface , ocelli piceous. Notum light 

 bistre-brown or pale fuscous, varied on the metanotum with pitch-brown, and sometimes 

 with a small yellowish spot near the peak. Dorsum of the abdomen light bistre-brown 

 or greenish grey, sometimes tinted in segments 8-10 with brown-ochre or raw-umber, 

 and with the joinings of the intermediate segments whitish: venter dull light sepia- or 

 olive-grey in segments 2-7 or 8, and either somewhat dull rubiginose (medium burnt- 

 sienna) or ochreous in the last two or three segments. Setae light sepia-brown, or dusky, 

 or brown-black. Eorceps-basis dull, either rubiginose or greenish grey : the limbs 

 blackish, with the last two joints sepia- grey. Femora light greenish grey, each with a 

 submedian triangular longitudinal black streak, which is acute inwards and acuminate 

 outwards in the hinder legs, but more rounded in the fore leg : fore tibia and tarsus 

 either sepia-grey or dark olive-grey ; hinder tibiae and tarsi sometimes of a lighter sepia-, 

 or greenish-grey than the fore legs, and sometimes of a yellower tint, with the extreme 

 distal edges of the short tarsal joints black, and with the ungues slightly rufescent or 

 greyish. When dried the femora in opaque view approach raw-umber brown in their 

 general hue ; in transmitted liglit the femora become strongly yellowish amber, and the 

 hinder tibia? pale yellowisli amber : the femoral streaks sometimes disappear. Wings 

 vitreous, varying considerably in the tint and extent of their coloration. 



In the typical semicolorata, Curt, [the semifmcta of Pictet] the membrane in the basal 

 half of the fore wing, and throughout the hind wing, is only faintly tinted witli dull 

 rusty yellow : in opaque view the neuration of both wings ajipears pitch-black, exceptino- 

 the extreme roots of the costa, sector (4), cubitus, prajbrachial, pobrachial, and anal (8), 

 the great cross vein, and the part between the roots and the bulla of the subcosta and 

 radius (3) of the fore wing, which are subtestaceous or rusty yellow ; in transmitted 

 light the whole of the neuration becomes in some positions light brownish, but in most 

 positions light brownish amber. 



Variation 1 [the semicolorata of Pictet, not of Curt.]. — The coloration of the fore 

 wing extends to the tip in tlie marginal and submargiual areas, and in the disk reaches 

 from the wing-roots to a little beyond the junction of the sector (1) and the fourth 

 sectorial intercalar nervure, the fork of the pi-aibrachial (G), and the anal angle, formin" 



