REV. A. E. EATON ON EECENT EPHEMEEIDiE Oil MAYFLIES. 29 



recurrent membi^ane at the fore-wing roots often prolonged into a narrow free-pointed 

 appendage beyond the peak of the naesonotum ; hind wing traversed lengthwise by a con- 

 tracted fold. Pronotuni compact, transverse, arched behind. Setce in $ short, smooth, 

 and usually glabrous ; in d very long, and more or less pilose. Forceps — limbs inserted 

 upon the sides of a laminar lobe extending from the distal ventral margin of the 9th 

 segment, which lobe is probably not deflexible, but is sometimes represented in the $ ; 

 their proximal joints the longest. Penis exposed, the lobes unarmed (excepting perhaps 

 in Lachlania) ; but stimuli capable of extrusion are in some genera concealed in the 

 9th segment. Proportions of eyes and ocelli vary with the genus. Fore legs of 6 short 

 and slender ; the tibia and tarsus often transversely rugose, the femur nearly as long as 

 the tibia, the ungues usually alike, the tarsus shorter than the femur; hind legs usually 

 the longest pair, the ungues subequal, broad, sometimes dissimilar, commonly flaccid. 



Nymi)h {OUgoneurla oulj). — Labium flat; abdominal tracheal branchia3 inserted in 

 the axils of notches in the posterior margins of the segments close to the lateral angles, 

 which angles are prolonged backwards. Pore legs strong, the femur and tibia densely 

 bearded beneath or behind with long hair, the tibia and tarsus slender in comparison 

 with the femur. The terminal margins of the fore wings are united by membrane 

 forming a hood. [I believe these characteristics are common to all the nymphs of this 

 alliance, judging from the structure of the adult flies.] 



{a.) Wing-membrane dull or satin-like ; fore wing with the anal nervure (8) forked, 

 and \\ith a free epinotal appendage ; 3 caudal setae. 



OLIGONEURIA, Pict. 1815. 



Illustrations. Adult (details) PL III. 2 a-6 ; (whole figures,) see citations of Costa, 

 Pictet, and Hagen (1855), under O. rhenana and O. anomala. Nymph, PL XXVI. ; see 

 also citations of Joly and Vayssiere (O. garumnlca), under O. rhenana. 



Adult. — Pore wing with 5 longitudinal nervures, beside the costa and subcosta (this 

 last concealed), and with several series of cross veiulets in the fore part of the wing. 

 Setae subequal in length to one another ; in 6 about 1^ as long as the body, and pilose 

 at the joinings ; in $ at most §, and at least \, as long as it. Eyes in s somewhat 

 reniform, and approximated to each other above ; in $ oval and remote ; anterior 

 ocellus not much smaller than the others. Spinose prolongations of the posterior lateral 

 angles of the abdominal segments slender, those of the 8th and 9th segments the 

 strongest. Thoracic spiracles open in the dried insect ; aperture of the anterior trian- 

 gular, that of the posterior ovate, narrowed below. 



Ni/mjjh [O. rlienana). — Six dorsal pairs of tracheal branchiiE, borne upon segments 

 2-7, and a ventral pair on segment 1, all alike composed of a small, thick, coriaceous, 

 subrotuud lamina, with a tuft of fibrils at its point of attachment. Divisions of the 

 labium intimately colierent : 1st maxilke furnished with a tuft of fibrillose tracheal 

 branchia; at the ouler base of the palpus. — In the nymph of O. rhenana, the bearding 

 of the fore leg is restricted to well-defined patches on the inner (or hinder) side of the 

 tibia and femur, the rest of the legs being almost quite glabrous ; the intermediate 



