250 EEV. A. E. EATON ON EECENT EPHEMERIDiE OR MAYFLIES. 



costa and the bases of the remaining nervures of the hind wing appear in most positions 

 of a light raw-umber or yellowish brown, and the rest of the neuration intense raw- 

 iimber approaching pitch-brown : the wing-membrane is faintly tinted with light raw- 

 umber throughout ; but the tint is chiefly noticeable in the hind wing and the basal half 

 of the fore wing, as in the Rhithrogena referred to above. Length of body 9 ; wing 10 ; 

 setae, s im. about 20 mm. 

 Hah. Colorado (M'Lach. Mus.) ; Manitou, Col. (Mus. Comp. Zool, Cambridge, Mass.). 



CiNTGMA GEMINATTJM, Sp. nOV. 



Suhimago (dried). — Very similar in aspect to Heptageiiia stilplmrea. Wings and 

 neuration in ? light yellowish ochre throughout ; in s the membrane is rather of a 

 yellowish grey, but the neuration is light yellowish ochre, though less strongly coloured 

 than in the other sex. Setae concolorous with the wings. Notum yellow-oclu*e varied 

 with lighter. Abdomen faded. Fore femur in 6 light brownish ochre, in ? Mars 

 yellow : tibiae and tarsi all whitish yellow-ochre, with the tarsal joinings and the 

 joining of the tibia with the tarsus light brownish ; in transmitted light the fore femur 

 becomes brownish amljer, the hinder femora and fore tibia light yellowish amber, and 

 the tarsi and hinder tibioe whitish amber. 



Imago [dried), $ . — Almost indistinguishable without inspection from Septagenia 

 sulphured, S im., and even when closely compared together the differences in colour 

 between the two species are trivial and few. C. geminativm has the vertex of the head 

 suffused with light reddish brown, no black spots near the eyes either on the vertex or 

 on the face, nor any at the bases of the coxae ; setoe uniformly whitish ; wing-neuration 

 for the most part piceous or bistre-brown instead of black, the stronger longitudinal 

 nervures amber-coloured towards the base ; wing-membrane vitreous, miiformly tinted 

 in the faintest degree with pale yellowish. Length of wing, d 8-9'5, ? 9-12 ; setae, ? 

 im. [the smallest specimen] about 18 mm. 



Hal). Washington Territory and (Lord Walsingham) California (in M'Lacb. Mus.); 

 Arkansas Canon, Col. (P. R. Uhler, in Mus. Comp. Zool. Cambridge, Mass.). This 

 species and Rhithrogena eleyantula are almost exactly alike in colour. 



RHITHROGENA, Etn., 1881 



Illustrations. Adult (details) Pis. XXIII. and XXIV. 43, see also citation of 

 Palmen (1884) under Rh. semlcolorata ; (whole figures) refer to citations of Stephens 

 (1835) and Pictet (1843-5) under the same, and of the latter under Rh. seinit'mcta. 

 Nymph, PI. LIV. ; see also citation of Pictet (1843-5) % Ba'etis % lateralis under Rh. 

 aurantiaca. 



Adult. — First joint of the hind tarsus equal to the second and a little longer than the 

 third joint; first joint of the intermediate tarsus a little shorter than the second, but 

 equal to the third joint ; first joint of the d fore tarsus much shorter than the second, 

 and this equal or subequal to the third joint ; first joint of the ? fore tarsus much 

 (about ^) shorter than the second, which is longer than the thu'd joint ; ungues mutually 



