EEV. A. E. EATON ON EECENT EPHEMEKID^ OR MAYFLIES. 215 



triaug'ular. Porceps-basis entire, or only slightly retuse, produced shortly between the 

 bases of the limbs and there split along the sides to admit the edges of their proximal 

 joints when the forceps close. Forceps-limbs 4-jointed ; 1st joint short, slightly com- 

 pressed, broader than the second, and forming a prominent projection inwards ; 2nd 

 joint the longest. Penis-lobes narrow and shortly beaked ; the orifice of the seminal 

 duct on the inner side of the beak is immediately interposed between the point of the 

 lobe and a small mov^eable appendage [stimulus], which together form the beak. Median 

 seta aborted ; lateral setse of ^ about 1|, of $ about IJ as long as the body. Oculi of 

 d obsoletely ascalaphoid, contiguous above during life. Vertex of $ head about as 

 broad as long, very little wider in front than behind ; the occipital border almost level 

 with the posterior orbits of the oculi. Median ocellus of j much smaller than the others, 

 isolated in a small deep depression in front of and below the anterior edge of the upper 

 surface of the head. Pronotum of ? broadly refiexed upon the mesoplevu'se, and with a 

 shallow curved median recess behind, which is not always distinguishable as a recess 

 when viewed from in front. 



A long-legged s])ecies in N. America \_S. tyincus] has the fore leg of the s about 1^ as 

 long as the body ; tarsus about thrice as long as the tibia, and this xf as long as the 

 femm' ; tarsal joints (as, a priori, probable in so attenuated a tarsus) slightly inconstant 

 in their relative lengths, but the first joint is equal in length to the second. Pore leg of 

 $ about -fr as long as the body ; tarsus about If as long as the tibia, and this | as long 

 as the femur ; the proportions of the first tarsal joint to the second are as 17 to 13. 

 Hind tarsus of s about If as long as the tibia, and this about f as long as the femur ; 

 its joints rank in lessening length 1, 2 subequal to 5, 3, 4, and the first is about ly as 

 long as the second joint. Median seta aborted ; outer sette in <s nearly twice as long as 

 the body ; in $ about If as long as the same. In other particulars this species is 

 normal. 



During repose the suhimago stands upon all of its feet, with the wings erect and setae 

 divergent. 



NympJi. — Very similar to Cloeon, but readily distinguished therefrom by having only 

 the foremost two tracheal branchiae on each side double, and by the endopodites appended 

 to the mandibles. — Abdominal tracheal branchiae foliaceous and diversiform, borne by 

 segments 1-7 and inserted each in a notch, close to the projection of the pleura, in the 

 posterior margin of the dorsum ; those of the first two segments formed each of tAvo 

 laminae narrowly connate at the base, the others of single lamintB ; their tracheae multi- 

 partite, except sometimes those of the hindermost. In nymphs of advanced grade the 

 venation, so to speak, of these organs is a useful aid to the discrimination of species ; 

 the figures in PI. L. illustrate sufiicieutlv the kind of dilferences noticeable. Antennae 

 it maturity about li-jointcd, not longer than the head and pronotum combined. 

 Mandibular lobes strong and fang-Hke ; the endopodite well developed ; stipes well- 

 oroportioned. Palpus of maxilla i. longer than the lacinia, finger-like [in fig. 1 the 

 irticular membrane of the proximal joining is shown as if distended by glycerine] ; the 

 irst joint a little longer than the second and longer than the third, the extremity of 

 vhich is acute ; lacinia narrow, oblique at the point, crowned with a tuft of hair and 



