KEV. A. E. EATON ON RECENT EPHEMERID.^ OE MAYFLIES. 227 



lobe of segment 9 is subtriangulav, with tlie apex shortly and acutely excised. Forceps- 

 basis of d entire, slightly retuse in the middle ; forceps-limbs 3-jointed, with the first 

 joint nearly thrice as long as broad, the second (the longest joint) somewhat gil)bons at 

 its inner base and slightly incurved, and the third joint short. Penis-lobes unarmed, 

 apparently combined into a single acute ovate lamellar iutromittcnt organ, concave above 

 and terminating with a single seminal pore. Median caudal seta atrophied ; outer setae 

 in both sexes f to | as long as the body ; those of the ? suhimago, from | to f as long as 

 the body. Oculi of 6 undivided, nearly contiguous above. Vertex of $ head somewhat 

 transverse ; the occipital margin raised slightly above the level of the posterior orbits 

 of the oculi. Median ocellus of ? isolated, a little smaller than the others. Pronotum 

 of ? of minimum proportions, reflexed only in the least degree upon the mesopleurae. 

 Nymph. — [PI. LII. was prepared from a cast slough, and consequently a small but 

 appreciable amount of distortion must be allowed for in some of the figures.] Body 

 stout, tapering in its posterior half ; integument extensively but very minutely granu- 

 lated or scabrid. Abdominal tracheal branchiae, in specimens of advanced grade, 

 completely obtected by the convex mesouotal shield (referred to above in the Sectional 

 description) and \_fide Walsh] decumbent upon the dorsum in the cavity enclosed 

 thereby; their insertions in segments 2-G are successively aj)proximated to one another 

 by small degrees. The said shield (in which the fore wings are immersed) dilFers merely 

 in its larger development from those of the nymphs of OligoneuHa and Ephemerellu 

 (already described), occupying, as it does, not onXj the interspace between the terminal 

 margins of the wings, but also surrounding their extremities and extending laterally 

 beyond their costal margins to the borders of the dorsum, in which respects it is doubt- 

 less in agreement with that of Prosopistoma. The lateral margins of the shield are 

 flanged, in continuity Avith the narrowly dilated pleural margin of the mesothorax, to fit 

 closely those of the subjacent segments ; its posterior edge, somewhat cordately sinuate, 

 is received into a slot or furrow in the front of a correspondingly undulated ridge 

 traversing the anterior part of the dorsum of the sixth segment, which is the longest by 

 far of the segments. [In figure 1, owing to displacement in the moulted integument, 

 this is overlapped by the shield, which nearly attains the posterior border of that seg- 

 ment.] In moulting the shield splits longitudinally in the middle ; on each side of it 

 two large slightly compressed straight prickles arise, one in the midst and the other at 

 the lateral border a little anterior to it, sloped in front but steep behind, their bases 

 being prolonged forwards ; of these the intermediate are the smaller. Above each of 

 the fore wing-roots is a small triangular tubercle. Head shortly bicornute in front ; 

 the spikes, horizontally prorect, slightly divergent, and either smooth or (one or both of 

 them) unidentate on tlie inside near the point, arise from above the anterior border of 

 the upper part of the head, which, viewed from below, forms a prominent transverse 

 ledge emargiuate in the middle and receding at the sides. Gcnoe acutely prominent 

 below the orbits. Antenna) 7-joiuted; the last three joints and the second joint are 

 longer than the others. During life {fide Walsh) the antenna; ai^e deflexcd and lie back 

 in grooves below the oculi. Lobes of the mandibles strong and fang-like ; endopodite 

 well developed ; outer edge of the stipes minutely eroded. Palpus of maxilla i. shorter 



