10 ;June, 



8. — Hinder tarsi equal in length to, or longer than, the tibise. Tarsal claws all 



narrow and hooked Siphlurus. 



Hinder tarsi shorter than the tibiae ; one claw obtuse, the other hooked in every 

 tarsus 9. 



9. — Basal joint of the fore tarsus much shorter than the next joint in both sexes... 



10. 



Basal joint of the $ fore tarsus much shorter than the next joint ; that of the 

 $ fore tarsus only a little shorter than the next. Femora sometimes dark- 

 banded, spotless. Basal joint of hind tarsus longer than, or equal in length 



to, the next joint 11. 



10. — Basal joint of hind tarsus equal to the next joint. Femora usually marked 

 with a dark median spot. Wings of sub-imago uniformly light greyish ; 

 transverse neuration rather fine Mhithrogena. 



Basal joint of hind tarsus shorter than the next joint. Femora either without 

 markings, or with only very faint bands. Wings of sub-imago light yellowish, 

 becoming striped transversely with grey before the moult ; transverse neura- 

 tion moderate Heptagenia. 



11. — Penis lobes broadly dilated at the tip. Wings of sub-imago greyish, with 

 rather strong transverse neuration, becoming striped transversely with dark 



grey before the moult Section A of Ecdyurus, Wos. 34 — 36. 



Penis lobes small, obvate. Wings of sub-imago uniformly grey, never striped ; 

 transverse neuration rather fine Section B of Ecdyurus, No. 37. 



In the following list of the British species, the synonymy is 

 limited to names in the Entomological Society's Catalogue of 1870 

 that have become obsolete, and the bibliographical references to the 

 Monograph on the Ephemeridce in Trans. Ent. Soc. Lond., and the 

 Revisional Monograph in Trans. Linn. Soc, Lond., above mentioned. 

 Eor brevity these three publications are here cited as " Cat.," " Mon.," 

 and " Revis.," respectively ; the date of publication in the Revision 

 alone is stated in parenthesis. 



1. Ephemera vulgata, Linne: Mon., p. 68, pi. iv, 5, 5b [adult details] ; 



Eevis., p. 59, pi. viii, 12b [adult details], and xxx [nymph] (1884). 

 The piceous dorsal markings of the best-marked abdominal segment comprise a 

 large pair of acute triangular spots, pointing backwards from the base, and a shorter 

 pair of fine lines between them also from the base. 

 Summer. Rivers. 



2. Ephemera danica, Miiller : Mon., 72, pi. jv, 8, 8a [adult details] ; 



Revis., 61, pi. viii, 12a [adult details] (1884). 

 The dark markings of the chalky- white abdomen comprise on the dorsum of the 

 best-marked segment a pair of moderately broad sub-lanceolate streaks, shorter than 

 the segment, from the base, with a shorter pair of very narrow streaks between them ; 

 the markings on each side sometimes coalesce, and are either lacking entirely, .or else 

 are reduced to a single pair of triangular spots in the anterior segments. 

 Summer. Streams. ' 



