SYNOPSIS OF THE BRITISH EPHEMERID^. 17 



Sub-imago straw-yellow ; mesothorax and metathorax 

 with a black stripe on each side, which have between 

 them a rhomboidal spot ; wings dull yellowish-grey, 

 with a few dark spots in the middle. 

 Habitat London. 

 Stephens probably united this species with E. vuJgata ; 

 I have before me only two English specimens of the sub- 

 imago. 



POTAMANTHUS, Stephens. 

 (Ephbmbra, Stephens (partim) -J Baetis, Stephens (partim). 



Head rather small ; eyes of the male double, large, far 

 apart ; wings four, unspotted, with numerous fine, 

 transverse veins; males with four-jointed anal forceps; 

 penis double; egg-valve long; three long caudal 

 filaments of equal length ; first tarsal joint very short. 



Larva short, roundish ; maxillarv oro^ans and leo:s slig^ht ; 

 on each side are six branchial plates, sometimes with 

 branchial setse ; three long caudal filaments. 

 The larva swims freely ; at least some of them do so, and 

 occurs in stas^nant water or sluo-crish streams. 



1. p. marginatus, L., Zetterstedt ; Eph. stigma^ Stephens, 

 56, 3, $ imago; E2)h. talcosa, Stephens, 57, 4, $ 

 imago. 

 Imago. Head and thorax shining black ; abdomen 

 dark brown, the posterior segments with pale annula- 

 tions ; caudal filaments brown ; legs yellowish-brown ; 

 the joints darker; anterior legs black-brown, the tarsi 

 brov.n. Wings hyaline, the apical half and the costa 

 rather smoky, the apical third of the marginal field 

 brown, with rows of irregular double cells ; venation 

 yellowish-brown ; anal forceps pale brown. 

 1863. c 



