SYNOPSIS OF THE EPHEMERID.E 13 



Wings two in number. Eyes alike in both 



the sexes and rounded evenly. Fly very 

 small ....... CSENIS. 



3. Eyes alike in both sexes, and rounded evenly. 



Fly of a large or moderate size . . 4 



Eyes rounded evenly in the female, but 



intersected transversely by an impressed 

 line in the male (excepting, perhaps, in 

 Habrophlebia, which is a fly of small size) 5 

 4. Wings usually spotted. Sexual forceps-limbs 

 of the male four- jointed, with the basal 

 joint short and the next joint much the 

 longest . . . . . EPHEMERA. 



Wings spotless. Forceps-limbs of the male 



three- jointed, with the basal joint much 

 the longest . . . POTAMANTHUS. 

 5. Front edge of the hind-wing somewhat arched, 

 scarcely at all receding in the middle of 

 the curve ...... 6 



Front edge of the hind-wing strongly angu- 



lated nearly in the middle, and with a deep 

 sinus or recess immediately beyond the 

 angle. Forceps-limbs of the male three- 

 jointed ; the basal joint, shorter than the 

 remainder, is dilated inside at the base; 

 the other two joints are rather long, and 

 resemble those of a finger . HABROPHLEBIA. 

 6. Forceps-limbs of the male three- jointed, with 

 the basal joint much larger than the re- 

 mainder .... LEPTOPHLEBIA. 



Forceps-limbs of the male three-jointed; 



the intermediate joint much the longest, 

 the other joints very short . EPHEMERELLA. 

 7. Tarsi of the hinder pairs of legs four-jointed. 

 Eyes of the male divided into two unequal 

 parts ; the upper segment, cylindrical or 

 somewhat turbinate, is facetted only on 

 its terminal surface ; the lower and much 

 smaller segment, of oval form, is facetted 

 all over with facets of less diameter than 

 those of the other segment. Fly small . 8 



