[September, 
the second supplementary rib and the third vas internum are more 
numerous, and the veinlets from the third vas fewer in number, than 
the last genus ; and, lastly, these veinlets are usually opposite to one ^ 
another. 
Genus Potamanthus, Pictet, restricted. 
Syn. Potamanthus, Pict., part. 
Type P. lutea, Lin., Pict. 
Distrib. — England, Italy, Germany, 2 sp. 
The second vas internum near the base of the wing anastomosei 
with the third, instead of with the first, as in Ephemera. The thin 
after receiving the second, gives off a simple vein on each side. Poi 
terior to the third vas internum there is, at the fewest, one bifid veinlet' 
[? from the recurrent vein of the third vas]. This genus is further 
distinguishable from Ephemera by the ascalaphoid eyes of the male,! 
and by his three-jointed forceps, whose proximal joints are much longer 
than the other two together. 
Genus Leptophlebia, Westwood. 
Syn. Potamanthus, Pict., part. 
Baetis, Burm., Pict., part. | 
Type L. vespertina, Lin. I 
Distrib. — Lapland, Italy, England, Austria ; Canada, United' 
States, Newfoundland. New Zealand, Australia, Ceylon, Cape of Good k 
Hope. c 
The vas ulnare consists of a simple posterior, and a bipartite an- ^ 
terior rib. Of the divisions of this last the foremost is bipartite at the 
commencement of its second fourth, and includes in its fork two or '' 
three supplementary veins and veinlets ; whilst the other is bifurcate, 
and includes one such vein. A supplementary rib, very like the pos- 
terior ulnar rib, intervenes between the vasa interna and the vas ulnare. . 
It is preceded and followed by two shorter veins. These last are united, ', 
either with the supplementary rib or with the first, very convex, vas ' 
internum. The former arrangement prevails in species inhabiting 
the southern hemisphere (which also usually have the marginal and ' 
sub-marginal areas coloured), the latter in the larger of the American | 
and European species. Eorceps three- or four-jointed, the basal joint 
the longest. Eyes of the ^ double.* The central seta is rather the 
longest. 
* Ascalaphoid. 
