24 [June, 1881. 



and 9, 2 , 4, 9*5, 8, 5, and 10 ; hinder feet nearly as 3, 3, 3, 2, and 7. 

 Two caudal seta?, usually twice, or twice and a half as long as the 

 body. Penis-lobes narrow, very slightly enlarged at the tip. 



Wings of sub-imago usually unicolorous greyish, the nervures not 

 conspicuously darker. 



Nymph with seven pairs of abdominal tracheal branchiae ; the 

 first "pair very large, ventral, the laminae broad, slightly curved, flat- 

 tened, and contiguous at their tips with one another beneath the base 

 of the abdomen ; the next five pairs lateral, their laminae deflected, so 

 as to be almost out of sight from above ; the last pair meet one another 

 underneath the body, and their laminae are folded lengthwise : tracheae 

 not obvious ; the fasciculated fibrils are scarcely two-thirds as long as 

 the laminae. Head much flattened, somewhat transverse : labruin 

 distinct, small. Mandibles terminated by a single, large, acutely- 

 triangular fang, with a smaller tooth at its inner base ; the former 

 nearly half as long as the interval between the base of the latter and 

 the point of the molar tuberosity. First joint of the upper maxillary 

 palpus largely dilated behind, and about half as long as the second 

 joint, which is slightly dilated before the tip. Lateral lobes of the 

 tongue narrower than the median lobe. Caudal setae three, subequal 

 to each other. Type, Bh. semicolorata (in Baetis), Curt = Baetis, 

 Walsh, Section C. Pictet, Mon. Ephem., pi. 21, f. 1, seems to be a 

 nymph of a Bhithrogena ; but I think B. lateralis, to which he refers it, 

 is a species of Ecdyurus. Distrib , Europe and ~N. America to Oregon. 



Heptagenia, "Walsh (restrict.). 



Imago. Hind tibia of $ about twice and a half as long as the 

 tarsus, whose proximal joint is about one-eighteenth as long as the 

 tibia. Eore-tarsus in <$ about once and two-thirds, in 2 about two- 

 thirds, as long as the tibia ; the proximal joint in $ about one-four- 

 teenth, in 2 about one-eleventh, as long as the tibia. Relative lengths 

 of the tarsal joints :— fore-foot, $ , 4, 28, 28, 18, and 7*5, 2 , 4*5, 10, 

 8, 3-5, and 7 ; hinder feet, $ , 2'5, 4, 4, 2'5 or 2, and 8. Two caudal 

 setae, usually in $ twice, in 2 once and a half, as long as the body. 

 Penis-lobes rather broad and divergent from one another. 



Wings of sub-imago usually of a yellowish tint, and at first almost 

 unicolorous ; in the next place the cross-veinlets become darkened ; 

 and still later, transverse fasciae and streaks of a similar dark greyish 

 hue are developed in the disc of the wing. The sub-imago in repose 

 erects the wings, and stands upon all of its feet, with the setae 

 divergent. 



