SYNOPSIS OF THE BRITISH EPHEMERID^. 33 



the male ; but the caudal filaments are unicolorous 

 pale, which makes their identity a little doubtful. 

 Length of the body $ 2h lines; expansion of the wings 

 $ 65 lines ; setse $ 6 lines. 



I considei' as the sub-imago of this species some specimens 

 which are of the same size and form of wincr, but they are 

 throughout of a dirty yellow, the caudal filaments with 

 darker annulations ; wings dull yellowish-grey, with the 

 costa little darker. 



Habitat near London, in June. 



The description is made from English specimens, which 

 have not been compared with the types. I noted that C. 

 cognatum, dhnkliatum and virgo (partim) were identical. 

 The description of C. cognatum agrees, but the short caudal 

 filaments indicate females, whereas the types are males. 

 Tlie yellow spot on the side of the prothorax in C. dimi- 

 diatum I could not perceive, but the specimens are much 

 shrunk. According to the description of C. virgo it should 

 have unicolorous caudal filaments, otherwise there is nothing 

 against its identity. 



Of this species I have only seen English specimens. 



4. C. PUMILUM, Burmeister, Pictet, Ephem. 253, 4, tab. 

 40, fig. 2 ; Baetis hioculata, Stephens, Qb, 12, $ 

 imago ; B. fuscata, Stephens, 66, 13, $ imago. 



Imago. Head and thorax shining dark brown; abdo- 

 men white, the tip brown ; caudal filaments white ; 

 anal forceps white, with the base broad; legs white, 

 tip of the femora darker ; wings hyaline, venation 

 delicate and pale ; apex of the marginal field Avith a 

 i'ew straight transverse veins. 



Female similar to the male' throughout ; only the abdomen 

 is unicolorous black-brown above and pale beneath. 

 1863. D 



