AQUATIC INSECTS 919 



12 (8) The third anal vein with a simple tenninal fork and unattached to the 



hind margin, although a few isolated short intercalaries 

 he between; in the wider posterior fork of the median vein 

 there is no cross vein before the origin of the intercalary; 

 male forceps three-jointed Potamanthus. 



13 (i) The cubital and first anal veins parallel at base (in a few forms with 



reduced and scanty venation, appearing a little diverg- 

 ent) . . . 14 



14 (15) Hind tarsi with five freely movable segments; eyes of the male simple 



and remote; venation never greatly reduced; intercalary 

 veins between the first and second anal veins unattached 

 basally and in two pairs, of which the pair nearer the hind 

 angle is the longer Heptagenia. 



15 (14) Hind tarsi usually with but four freely movable segments, the basal 



segment being more or less completely consohdated with the 

 tibia; eyes of the male enlarged, often approximated on the 

 dorsal side and divided into superior and lateral portions 

 with corneal facets of different size; venation various, 

 sometimes greatly reduced; intercalary veins between the 

 first and second anal never as above 16 



16 (17) The three anal veins nearly parallel to the hind margin of the wing 



and to each other, ending in the outer margin; in the hind 

 wing the branches of the radial vein are strongly unilateral 

 on the anterior side . . . Baetisca. 



17 (16) Anal veins strongly divergent distally, usually both the second and 



the third ending in the hind margin; forks of the radial vein 

 in the hind wing more symmetrical 18 



18 (39) The posterior division of the median vein with a normal posterior 



fork; hind wings, when present, usually but httle longer 

 than broad and with a copious venation. . . . 19 



19 (32) The intercalaries between the first and second anal veins variable, 



but usually more or less independent, and not directly 

 dependent from the first anal; three weU-developed caudal 

 setae (except in Blasturus, in our fauna) 20 



20 (31) Hind wings present 21 



21 (28) Bisector of the posterior fork of the median vein and bisector of the 



cubital fork unattached basally; between the latter and 

 vein Cu2 no intercalaries; vein Cu2 in the hind wing rarely 

 preserved; caudal setae generally much longer than the 

 body; penultimate segment of the male forceps shorter 

 than the antepenultimate 22 



22 (27) In the hind wing the subcostal vein reaches nearly to the wing apex; 



male forceps three-jointed 23 



23 (26) Hind wing with a slight concavity at the middle of costal margin; 



five to six longitudinal veins between Mi and M2; veinlets 

 numerous about the wing margins and cross veins numerous 

 in the hind wings. 24 



24 (25) Third anal vein of the hind wing wanting; caudal setae of about 



equal length Leptophlebia. 



