82 REV. A. E. EATON ON RECENT EPHEMERID,^ OR MAYFLIES. 



is curved in correspondence, but in the latter it is usually almost straight, and often 

 subparallel with the abruptly abbreviated costa. Metathoracic spiracle straight-lipped ; 

 the valves usually closed, or connivent, in dried specimens : mesotnoracic spiracle larger, 

 the aperture narrow, and sometimes furnished with a very minute guard at its anterior 

 corner, the lips unequal, usually gaping a little in front, the uppermost strongly vaulted 

 and (when the guard is absent) often bent round the front of the aperture. Pronotum 

 of ? closely appressed to the mesonotum, longitudinally cariuate, and posteriorly excised 

 or retuse in the middle. Forceps-limbs inserted at the sides of the terminal border of a 

 transverse, and commonly deflexible, lobe extended from the segment, termed the 

 "forceps-basis," and represented by a projecting lamina in the ? , termed the "ventral 

 lobe of segment 9." Eyes of 6 ascalaphoid ; anterior ocellus rather smaller than the 

 others. Subimago quiescent during many hours, standing (so far as observed in 

 European genera) upon all of its feet, with wings erect, and with the lateral caudal setae 

 spreading, or divergent from the middle seta. 



Section 5 of the Genera. — Type of Leptophlehia. Adult. — Pronotum of $ traversed 

 lengthwise by a raised median line or fine ridge, and excised (or at least strongly 

 emarginate) in the middle of its posterior border. Hind tibia usually longer than the 

 femur, rarely subequal to it ; the tarsus shorter than the tibia. Eirst axillary nervure 

 (9') in some degree convergent towards the second axUlary (9-) near the base of the fore 

 wing [not obviously so in PI. XII. 19, Choroterpes]. Nymph [out of nine genera in this 

 Section four are imknown]. — Wings free along their terminal margins. Palpus of 1st 

 maxilla longer than the lacinia, which is crowned with a dense tuft of hair, and ciHate 

 on the inner edge below the point. Lobes of the labium smaller than the laciniae of 

 the 2nd maxillae. Abdominal segments 1-7 furnished with tracheal branchiae, those of 

 the first segment erect. Hinder lateral angles of the posterior segments slightly pro- 

 duced. Natation laboured, aided by movements of the legs. 



To exclude the possibility of the figures of wings being supposed to afford precise 

 characteristics of genera, suitable for employment in analytical tabulation, variations of 

 the most obvious features of the neuration are tediously noted in the generical descriptions. 

 The variations in every genus proceed metliodically, not at random. In view of the 

 consequent prolixity of the descriptive text, the following aid to the determination of 

 genera may be referred to with advantage when adult specimens require assorting. 



Analysis of Geneba of the Leptoplilebia Type : — 



Hind wing in front somewhat 



arcuate; tarsal claws all narrow and hooked Atalophlebia. 



depressed in the middle ; each tarsal claw unlike the other ; median caudal seta 



subequal to the others Leptophlebia. 



far shorter than the others Blasturus. 



strongly angulated ; tarsal claws 



all narrow and hooked ; basal joint of forceps-limb longer than the remainder Adenophlebia. 



