EEV. A. E. EATON ON EECENT EPHEJIERn)^ OR MAYFLIES. 115 



wing contains from 2 to 5 intercalar nervures ; when there are five, 1, 3, and 4 are abbre- 

 viated or obsolescent ; when four are present, intercalar 3 is absent ; Avhen there are three, 

 1 is the short one : intercalars 2 and 5 are constant, they communicate by cross veinlets 

 with each other, and usually with the anal (seldom the first axillar) nervure, and either 

 of them may terminate abruj)tly or else (combining intimately with a cross veinlet) may 

 bend suddenly aside to join an adjacent nervure ; for example, intercalar 5 may be 

 isolated, or may bend suddenly aside to intercalar 2 or to the anal ; and intercalar 2 may 

 be abrupt and communicate by cross veinlets with the anal nervui-e alone, or may bend 

 suddenly aside to join either the anal or intercalar 5. Orifice of the mesothoracic spi- 

 racle usually closed in the dead insect ; when open, the aperture is small, gaping in front, 

 and without a guard. Forceps-limbs of d 3-jointed, the proximal joint shorter than the 

 others combined, and suddenly dilated or tuberculated on the inner side of the base ; the 

 second and third joints rather long, and like those of a finger. Forceps-basis bifid, 

 narrowly or acutely excised in the middle ; the homologous lobe of ? also bifid and 

 acutely excised. Caudal setae in both sexes 3, mutually subequal, and thrice as long as 

 the body. Ungues in every tarsus dissimilar each to the other ; fore tarsus in s little 

 longer than the tibia, which is nearly ^ longer than the femur ; its joints in diminishing 

 order rank 2 subequal to 3 ; 4, 5, and 1. Hind tarsus about ^ as long as the tibia ; its 

 joints rank 5, 2, 3, and 4 ; 1 is ill defined ; hind leg not much longer than the inter- 

 mediate leg. Fore tarsus $ (exclusive of joint 1) about f as long as the tibia and joint 1 

 combined, which are about 1^ as long as the femur ; its joints rank as in the d hind 

 tarsus ; 1 is indistinctly defined, j^ymph latent in places where the current of shallow 

 streams is gentle, or where the ripple from rapids is greatly diminished amongst stones 

 at the brink. Abdominal tracheal branchiae nearly uniform in shape, bifid, with the 

 divisions filiformly dissected, and each with fewer segments in the upper division than in 

 the lower ; when extended they slant backwards and outwards, with the smaller divisions 

 ascending ; then- segments vary in number with the age of the nymph, and are most 

 numerous in the intermediate pairs ; theii- surface is sparsely beset with minute hairs. 

 Mandibles, labium, and maxillte ii. very similar to those of Blasturus ; maxillae i. nearly 

 as in Tlwaulus. Tongue obcordate-oblong ; paraglossse narrow, curved, oblique and 

 acuminate laterally, with a slight indentation in the margin a little before the point. 

 Body slender ; antennae of moderate length ; posterior lateral angles of segments 8 and 9 

 of the abdomen shortly and acutely produced ; caudal setae about f as long as the body, 

 and beset with minute spreading hairs at the joinings. Hind leg about as long as the 

 fore leg ; the tarsus (claw excluded) almost \ as long as the tibia. 



Type. S.fusca (in Ephemera), Curt. 



Distribution. Europe, temperate and southern ; N. America, New Hampshire (im- 

 described sp.). 



Etymolorjy. k^pic and <pAe/3iov, in reference to the prevailing delicacy of the cross 

 veinlets of the wings. 



The figures in PI. XIII. of this volume do not display the mutual dissimilarity of the 

 tarsal ungues ; they were drawn from dried specimens. This feature of the ungues was 

 stated correctly in Trans. Ent. Soc. Loudon (1871), p- 90, but not in Ent. Mo. Mag. 



