50 Rey. A. E. Haton’s Monograph 
Oculi even in both sexes . 14 
102 Oculi in ¢ ae polapholes WslOey "intersected by a slightly i im- 
pressed line. “ 11 
Penultimate segment in beneath prtonged into a short 
iBT lamellar process ; . . 
Penultimate segment in 9 beneath simple ; Potamanthus, 
1PAL, OT 3% Ie 
Proximal joint of leg of forceps of ¢ short . 13 
122 Proximal joint of leg of forceps of ¢ the longest ; Gen. OMe 
B23 - Leptophlebia, Piet) 2-2: 
13 Hinder tarsi 4-jointed; Ephemerella, Pl. I. f. 5. 
Hinder tarsi 5-jointed; Coloburus, Pl. III. f. 3. 
Penultimate segment in § beneath prolonged into a short 
14 lamellar process . : : ; 
Penultimate segment in 9 beneath simple c : : 16 
Cross-veinlets crowded, indistinct ; Botisca, Pl. IT. f. 6. 
1} Cross-veinlets regular, well-defined ; Tsonychia, Pl. IIT. f. 4; 
Heptagenia, Pl. III. f. 5. 
16 3 long caudal sete . < ‘ : : : . P - ey 
2 long caudal setz : : : : ; ; : 5 18 
Cross-veinlets crowded, well-defined ; Huthyplocia, 2 , Pl. 1.f.8. 
172 Cross-veinlets regular, well-defined ; Pentagenia, 2, Pl.1. f£. 6; 
Ephemera, Pl. I. f. 9. 
18 { Hinder tarsi 5-jointed ; ne Tk IML, 1, PA, 
Hinder tarsi 4-jointed .. : 5 » ws | 
Middle seta very short; Pentagenia, g, PILI. £6; Hexagenia, 
19 TEMG Te a Pc 
Middle seta rejected ; Palingenia. | 
Materials for a complete analysis of the genera of the 
Hphemeride are not at hand. Of some, only one sex is — 
at present known: jof others, only mutilated specimen 
deprived of legs, or examples with the legs shrivelled up 
in drying, so as to prevent their proportions being made 
out, are in Huropean collections. Our grounds for 
establishing comparisons between the genera are conse- 
quently very limited. 
In determining from the imago the affinities of a genus, 
the principal points to be noted are,—First, the neura- 
tion of the anterior wing; Secondly, the structure of the 
hinder pairs of legs ; and, Thirdly, sexual peculiarities. _ 
In the neuration of the anterior wing, the most im- 
portant features are the disposition of the nervures dis- 
