86 



[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, Pietet, restricted. 

 Syn. PotamantJius, Pict., part. 

 Type P. lutea, Lin., Pict. 

 Distrib. — England, Italy, Germany, 2 sp. 



The second vas internum near the base of the wing anastomoses 

 with the third, instead of with the first, as in Ephemera. The thii'd, 

 after receiving the second, gives off a simple vein on each side. Pos- 

 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 JEphemera 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, TVestwood. 



Syn. JPotamantTius, Pict., part. 



Baetis, Burm., Pict., part. 

 Type L. vespertina, Lin. 



Distrib. — Lapland, Italy, England, Austria ; Canada, United 

 States, Newfoundland. New Zealand, Australia, Ceylon, Cape of Good 

 Hope. 



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. Forceps three- or four-jointed, the basal joint 

 the longest. Eyes of the ^ double.* The central seta is rather the 

 longest. 



* Ascalaphoid. 



