84 



Day: Ephemeroptera 



3. Front of head rounded, lacking frontal process 



Campsurus Eaton 



— Head with a conspicuous frontal process 4 



4. Gills broad, laminate, tapering only near tips, with 

 many prominent lateral tracheal branches; marginal 

 fringe of hairs short, inconspicuous; mandibular tusks 

 curve downward apically in lateral view 



Ephoron Williamson 



— Gills narrow, tapering, with no distinct lateral tracheal 

 branches, margined on each side by a fringe of hairs 

 at least twice as long as width of gill; mandibular 

 tusks upcurved apically, in lateral view 5 



5. Frontal process of head entire; truncate, conical, or 

 rounded (fig. 3:2e; Z:3a,b) Hexagenia Walsh 



— Frontal process of head bifid 6 



6. Mandibular tusks crenate on outer (upper) margin; 

 labial palp 2-jointed Pentagenia Walsh 



— Mandibular tusks smooth on margins; labial palp 3- 

 jointed Ephemera Linnaeus 



Fig. 3:3. a,b, posterior and anterior third gill lamellae of 

 Hexagenia spp.; c, Hexagenia limbata californica, male genitalia; 

 d, Hexagenia sp.; male genitalia; e, Heptagenia sp.; male geni- 

 talia (a,b,c,e, Spieth, 1933; c, W. C. Day). 



Family EPHEMERIDAE 



Only one species of the entire family Ephemeridae 

 has been found in California, namely Hexagenia 

 limbata californica (Upholt) 1937. This species is 

 characterized as follows. 



Male adult. — Large, yellow, tinged with red on abdomen; 

 extensive dark color pattern. Fore tarsal joints red brown. 

 Costal area of fore wing light brown .Cross veins of fore 



wing from costa to M x and in hind wing disk, heavilj 

 marginated with black. Entire rear margin of hind wing 

 widely and heavily infuscated. Penes hook-shaped. Length 

 fore wing 17-18 mm. (fig. 3:3c). 



Nymph. — Fossorial, yellowish white, dorsum marked as 

 in adult; with low, rounded frontal process of head. Length 

 of mature nymph, 20-27 mm. 



Distribution: Sacramento and San Joaquin river systems. 



Family HE PT AGE N IID AE 



Key to the Genera 



Adults 



Outer fork (Of) of Rs of hind wing wanting; male forceps 



5-jointed Arthroplea Bengtsson 



Outer fork of Rs of hind wing present; male forceps 



4-jointed 2 



Fore tarsus of male not more than 3/4 as long as tibia; 

 apical margin of forceps base deeply excavated 



Anepeorus McDunnough 



Fore tarsus of male distinctly longer than tibia; apical 



margin of forceps base not as above 3 



Basal joint of fore tarsus of male 1/2 or less than 1/2 



as long as second joint 4 



Basal joint of fore tarsus of male at least 2/3 as long 

 as second joint; may equal or slightly exceed it in 



length 6 



Stigmatic cross veins more or less anastomosed; basal 

 joint of fore tarsus of male 1/6 to 1/4 as long as second 



(fig. 3:4a) Rhithrogena Eaton 



Stigmatic cross veins not anastomosed; basal joint of 



fore tarsus of male variable 5 



Basal joint of fore tarsus of male 1/3 to 1/2 as long as 

 second; penes more or less distinctly L-shaped 



Stenonema Traver 



Basal joint of fore tarsus of male 1/6 to 1/3 as long 

 as second; penes not distinctly L-shaped (fig. 3:3e) 



Heptagenia Walsh 



, Basal joint of fore tarsus of male 2/3 to 3/4 as long 



as second joint 7 



Basal joint of fore tarsus of male equal to or slightly 



longer than second joint 8 



Stigmatic area of forewing divided by a fine line into 

 an upper and lower series of cellules; basal costal 



cross veins very weak (fig. 3:46) Cinygma Eaton 



Stigmatic area of fore wing not divided as above; basal 

 costal cross veins usually well developed (fig. 3:5a) 



Cinygmula McDunnough 



Fig. 3:4. Fore wings, o, Rhithrogena flavianula; 

 b, Cinygma sp. (W. C. Day). 



