244 EEV. A. E. EATON ON EECENT EPHEMERID.E OR MATELIES. 



sepia or brown-black border surrounds the tip of the hind wing, and, narrowing gradually, 

 terminates anteriorly where the costa first comes into proximity to the subcosta, while 

 posteriorly its extremity is nearly coincident with that of the anal (8) nervure. Wing- 

 nem-ation, in opaque view, for the most part pitch-black ; but that of the colourless 

 portion of the hind wing is pale ; and in the fore wing the subcosta and radius outside 

 the pterostigmatic region, together with the interjacent cross veinlets and parts near the 

 subcosta of the cross veinlets in the adjoining portion of the marginal area, and also the 

 near extremities of the main nervures posterior to the radius, are light raw-umber. 

 Length of body 10 ; wing 13 ; setae, 6 im. about 35 mm. 



Jlab. Japan ; Yagohara, 29th July (G. Lewis, in M'Lach. Mus.). 



IROX, Etn., 1883 [in Plate XXIV.]. 



Illustrations. Adult (details), PL XXIII. 44 [Epeoriis] and PI. XXIV. 44 

 [/row]. Nymph, PI. LV. 



Adult. — First joint of the hind tarsus equal to the second and third joints respectively ; 

 the corresponding joints of the intermediate tarsus similai'ly proportioned ; first joint of 

 the c? fore tarsus longer than the second, which is equal in length to the third joint ; 

 first joint of the ? fore tarsus shorter than the second, and this equal to the tliird joint ; 

 ungues mutually dissimilar. Penis lobes apparently liable to be deformed through 

 desiccation ; in the typical species they are comparable to those of Thalei'osphjrus 

 (PI. XXIII. 40), but are not so broad ; but in the other species they seem to be tubular 

 and contiguous, somewhat as in Bleptus or species of BhUhrogena. — Fore leg of d about 

 as long as the body ; tarsus about 1^ the length of the tibia, and this about twice as long 

 as the femur; the joints in the order of their shortening rank 1, 2 equal to 3, 4, 5. 

 Fore leg of $ about as long as the body ; tarsus about | the length of the tibia, and 

 this about l-^-o as long as the femur; the joints in the order of their shortening rank 2 

 equal to 3, 1 equal to 5, 4. Hind tarsus of 6 about f as long as the tibia, and this very 

 nearly as long as the femur ; its joints in order of their shortening rank 5, 1-3, 4, and 

 the first three joints mutually equal in length are each about half as long as the fifth 

 joint. Ungues in every tarsus each unlike the other. Hind wings of ordinary form; 

 the axillar region narrow, but with sufficient neuration. In tlie ? al)domen the relative 

 lengths of the dorsal segments in dried examples maybe formulated thus : — 7, 9, 10, 10, 

 10, 10, 8, 6'5, 6 ; ventral lobe of the ninth segment slightly emarginate. Forceps-basis 

 of 6 seldom conformable to that of Mhithrogena, but usually tridentate, or saliently 

 curved behind between the insertions of the limbs. Penis lobes either as in Rhithrogena, 

 or else narrow and split lengthwise along their inner sides ; stimuli well developed in the 

 type, but not obvious in the other species, perhaps retractile. Outer caudal setge of 6 

 about 4 times, those of $ about twice, as long as the body. Vertex of the dried 2 head 

 transverse, convex from side to side : the occipital border when not refuse is scarcely 

 prominent in the middle, and almost even with the posterior orbits of the oculi ; median 

 ocellus somewhat isolated, prominent, but rather below the anterior border of the upper 



