102 Rev. A. E. Eaton’s Monograph 
@ simillima mari, processu ventrali segmentorum 
penultimi breviter inciso. 
Long. corp. ¢ 7-8, ¢ 6-8; set. d 9 im. 6-7, 9 
subim. 4-5; exp. al. ¢ 20-22, 9 22-25 mm. 
- Hab.—Illinois (Walsh) , Indiana (Say); and California. 
Genus CLOEON. 
(Ala mesothoracica, Pl. IT. fig. 7.) 
Ephemera, p., Lin. 1761; Cloeon, Leach, 1815 ; Cloe, 
p., Burm. 1839; Cenis, p., Walk. 1853; Chloeon, Lub- 
bock, 1863 ; Clocopsis, Htn. 1866. 
Nympha natans, laminis branchialibus utrinque sep- 
tem: laminarum septima simplex, cetere bilamellares, 
omnes marginibus integris. Palpi biarticulati, articulis 
longitudine equalibus; inferiores depressi, apicibus 
obliquis; superiores tenuissim1, filiformes. 
Alis erectis setisque divergentibus subimago quiescit 
stans in pedes omnes. 
Imago. Ale seteeque due. Oculi maris_ bipartiti, 
parte superiori sub-turbinata. Tarsorum _posteriores 
quadri-articulati ; articulorum primus multo longissimus, 
tibiz adnatus, secundus brevis, tertius brevissimus ; 
ungues dissimiles. Pes forcipis tri-articulatus, secundo 
articulorum longissimo: penis occultus. Ovivalvula 
femina caret. 
Cloeon dipterum. 
(Forceps, Pl. V. fig. 10.) 
Ephemera diptera, Lin. 1761. LE. striata & annulata, 
Miill. 1776. Cloeon pallida, Leach, MS., 1815. H. margi- 
nata, Gor. & Pritch. 1829. C. marmoratum & obscurum, 
Curt. 1834. C. cognatum, dimidiatum, virgo & consobri- 
num, Ste. 1835-6. Oloe diptera, Burm. 1839. Cloe affinis, 
Ramb. 1842. Cloe virgo & cognata, Pict. 1843-5. 
H. culiciformis, Fonscol. 1846. C. diptera & cognata, 
Walk. 1853. Chloeon dipterum, Lubbock, 1863-5; Cloeop- 
sis diptera, p., Ktn. 1866. 
Subimago, v.s.s. Alze pallide cervino tinctee. 
Imago, v. v. s. ¢&. Oculi turbinati sub-carnei, 
vel rufo-hepaticolorati; inferi atro-picei. Tergum tho- 
