EEV. A. E. EATON ON EECENT EPHEMEEID.E OE JIATFLIES. 123 



2nd segment and usually from the first as well; when they exist on segment 1 they are 

 minute, erect, hirsute, and filiform, unlike the others ; these, issuing from the posterior 

 margins of the segments at the bases of the pleurae, arc recuml)ent upon the sides of the 

 dorsum and either imbricated or stratified, and are formed each of a broad pergamentosc 

 lamina (or a memln-anous lamina, if the branchia be wholly obtected), concave on the 

 luiderside, covering and in some extent coherent Avith a forked appendage, the support of 

 membranous lamellae, which are numerous and closely imbricated in the large branchiae, 

 but very scanty in the small. Many of the pleurae are dilated so as to form acute serra- 

 tures at the sides of the abdomen, and their edges, like some other parts of the body 

 {e. g. the femora or setas), are l^eset witli remarkable hairs, which commonly resemble in 

 their structure the peculiar hairs of certain Troml)idiid Acar'ma in being filiform or 

 clavate, and in many instances microscopically velutinous or otherwise roughened. 

 Natation laboured, aided by movements of the legs. 



The genera of this section display afiinity with the type of Ccenis in the particulars 

 detailed in the last sentence but one of the foregoing paragraph. 



North America has yielded several nameless nymphs referable to tbis section, whose 

 ultimate development needs investigation. Their characteristic diiferences chiefly reside 

 in the arrangement and fonu of the tracheal branchiae, the length of the palpus of the 

 1st maxilla (when present) and the proportions of its component joints, and in the form 

 of the body — -tabulated hereunder. The indications of wing-neuration delineated in 

 their figures are largely conventional. Being for the most part very nearly akin to 

 Ephemerella, their detailed descriptions are inserted immediately after the descri])tive 

 letterpress of the species of this genus, preceding the description of the Cingalese genus 

 Teloganodes, whose nymph is unknown. Those are the only two genera in the section 

 that are named. 



Tabulation of Nymphs ranked in Section 6 of the Genera. 



Nos. 3-7 of the abdominal segments bear tracheal brancliise ; of these, the 

 first four ou each side of the dorsum are loosely imbricate. Antenuaj 

 inserted 



upou the disk of the frons. Terminal joint of the palpus of maxilla i. 



subequal to the remainder ; joint 2 longer than joint 1. Caudal 



setse narrowly plumose. Brauchial lamin;e oblique, oblong or 



ovate oblong PI- XXXVII. Ephemerella. 



scarcely i as long as the remainder; joint 2 subequal to joint 1. 



Branchial laminre somewhat obovate PI- XXXVIII. 1-10. 



scarcely I as long as the remainder ; joint 2 about | as long as 



joint 1. Branchial larainse subrotuud PI. XXXVIII. 11-15. 



in re-cnteTing angles at the front lateral margins of the frons. Ter- 

 minal joint of the palpus of maxilla i. about \ as long as the 

 remainder; joint 2 about | as loug as joint I. Brauchial laminae 

 somewhat oblong and slightly oblique. Ventral surface of the body 



singularly adapted for adhesion to smooth surfaces PI. XXXJX-. 



Nos. 4—7 of tlie abdominal segments bear tracheal bi'anchiae ; the laminae, 

 irregularly subovate, are compactly imbricate. Caudal setae plumose. 



