EEV. A. E. EATON ON EECENT EPilEMEEID.E OR MAYFLIES. 155 



in their fore wings, and this is especially noticeable in advance of the cubitus (4) in the 

 proximal half of the wing. Cloeon and Centroptilum cannot be distinguished from one 

 anotlier absolutely by their mesothoracic wings ; but several species of the former 

 genus can always be recognized by peculiarities of minor detail not essential character- 

 istics of that genus. The aforesaid iutercalar veinlets are paired in Baetis, in a few 

 exotic species of Centroptilum and Cloeon, and often in Callihcetis; their relative len"-th 

 is usually greatest in Baetis and Centroptilum, which, like Cloeon, have fewer cross 

 veinlets than CalUhcetls in advance of the cubitus in the proximal half of the winf. In 

 Baetis a short veinlet from the inner margin of the fore wing almost invariably meets 

 the second axillar uervure (9-) so as to form a small fork ; but the corresponding nervure 

 is simple in Centroptilum. 



In the Appendix will be found a statement of the classification of these genera, adopted 

 by me in 1868, which was accidentally omitted from page 20. 



The nymphs may be tabulated as follows : — 



Tabulation of Nymphs of Section 9 of the Genera. — Type of BAiins. 

 Abdominal tracheal braucliice all simjjje ; the laminse 



broadly obovate, obtuse. Terminal joint of the palpus of maxilla ii. 

 rotund, forming with the penultimate a clavate mass indented on the 

 inner side at the joining. Terminal joint of the palpus of maxilla i. 



long PL XLIV. Baetis. 



partljr oblong and partlj' ovate-lanceolate, oblique and acute. Terminal 

 joint of the palpus of maxilla ii. short and elhpsoidly rounded at the 

 tip, forming with the penultimate joint a simply clavate mass. 



Terminal joint of the palpus of maxilla i. very short PI. XLV. Nameless Gen. 



partly Hnear-obovate-lanceolate, and partly broadly so, acute. Ter- 

 minal joint of the palpus of maxilla ii. quach'angular, forming with 

 the penultimate joint a compressed clavate mass broadly and abruptly 

 truncate at the end. Terminal joint of the palpus of maxilla i. long 



and slender PI. XLVI. Centroptilum. 



Abdominal tracheal branchiae mostly, or all, conduplicate with unequal 

 segments ; the larger segments of the laminas 



irregularly subrotund ; the laminse of the hindermost branchiae single. 

 Terminal joint of the palpus of maxilla ii. large and compressed, 

 forming with the penultimate joint a compressed clavate mass 

 obliquely truncate and acute at the extremity. Palpus of maxilla i. 



triarticulate, with the terminal joint long and slender PI. XLVII. Cloeon, 



of the first and second of the series somewhat contorted ; those of the 

 3rd to 6th obliquely subovate ; that of the seventh elongate-oval ; all 

 of the laminae are duplicate, but the lesser lobes arc much smaller in 

 most of the series than those of Cloeon. Terminal joint of the palpus 

 of maxilla ii. small, forming with the penultimate joint a narrow 

 slightly compressed mass, acute at the point. Palpus of maxilla i. 

 (in alcoholic specimens) 2-jointed, with the last joint loag; but if 

 ever triarticulate, the terminal joint would be minute [the joining 



might have been obliterated in the samples examined] PI. XLVIII. Callibcetis. 



21* 



