138 EEV, A. E. EATON ON EECENT EPHEMEEID^ OE MAYFLIES. 



TRICORYTHUS, Etn. 1868. 

 Illustrations. Adult (details), PI. XV. 25 ; (whole figure) see citations of Saviguj 

 and Pictet under T. varicauda. Nijmfh (?), PI. XLI. 



Adult. — Hind wings absent. Caudal setie 3, mutually subequal in length, about ai 



long as the body in ? , and twice as long in 6 . Cross veinlets multiserial, numerous ii 



the midst of the wing and of the marginal area (but rudimentary in the latter), remot( 



from the terminal and inner margins ; these margins are devoid of isolated rudiments o 



veinlets, and the longitudinal nervures of branchlets. The anal-axillar interspace contain 



two well-developed intercalar nervures ; the nearest to the anal (8) nervure describes ; 



simple curve, and meets the first axillar (9^) at a point nearly in a line with the junctioi 



of the branches of the pobrachial (7) nervure, and of the sector (4) with the cubitus (5) 



and at a distance from the inner margin of about f of the interval between its owi 



extremity and the costa ; the hinder intercalar meets the anterior near its inward termi 



nation, and its extremities are curved slightly in opposite directions, somewhat like th 



stem of an italic y*; hence the intercalars simulate a deeply forked nervure annexed t 



the first axillar. The recurrent membrane of the wing-roots does not extend beyond th 



point of the scutellum. Ventral lobe of ? segment 9 obtuse. <s unknown to me ; pre 



portions of legs unascertained. Ni/nqih [Ccenis maxima, Joly, is perhaps a Tricorythut 



and is provisionally described as such, pending identification]. — Body broadest at th 



mesothorax ; head slightly narrower than the prouotura, and somewhat similar in contou 



to that of an Ephemerella. Pronotum quadrangular, oblong, with sharply defined angle: 



Abdomen slender in comparison with the anterior portion of the body, broadest about tli 



4th segment, and tapering slightly posteriorly, but nearly as broad in front ; segmeni 



2-5 combined are about \ as long as the posterior segments united ; dorsum arched 



venter slightly convex ; pleurae somewhat dilated, and similar in character to those ( 



Ephemerella, but less obviously cUiated, their hinder angles acute in the anterior sej 



ments, but gradually more and more prolonged and acuminate in the posterior segment 



Dorsal tracheal branchiae issue from the antero-lateral angles of the 1st segment, froi 



the posterior margins at the bases of the pleurce of segments 2-5, and from the disk ( 



the 6th segment at a point in line with the insertions of the four preceding ; those ( 



segment 1 [teste Vayssiere], lost in examples examined by me, are minute, subulat 



hirsute, jointed close to their insertion, and erect ; those of segment 2, large, elytro: 



and coriaceous, obtect the hinder pairs completely, and are hitched together by the 



adjacent inner edges, where a row^ of short stiff ascending hairs inserted along the margi 



of the right elytron is caught by a flange projecting from beneath the margin of the le 



elytron ; moi'eover the same elytroid laminae are securely held down anteriorly by tl 



hind margin of the segment, which is bevelled or under-cut to receive their front edge 



and has a small projecting triangular tooth in the middle, affording further support ; eac 



elytron, subquadrate in the main, with the outer side and the angles adjacent therei 



rounded off, is externally convex and nude, ciliated with hairs of peculiar form along i 



outer and terminal margins, and is traversed obliquely by a ridge running from the pla( 



of attachment towards its inner posterior angle ; each on the imderside is largely concav 



