SYNOPSIS OF THE BRITISH EPHEMERID^. 9 



even to Baetis and CloeoUy although the presence of three 

 caudal filaments is expressly given as the generic character. 

 The genus Ccenis with seven species is divided by Stephens 

 into two sections, with long or short (^Brachycerus) caudal 

 filaments. That this character was only sexual seems to 

 have escaped him. Baetis includes eighteen species, of 

 which, however, the eight last wdtli faint venation belong to 

 Cloeon. Finally, in Clo'eon he has eight species. 



My comparison of the types has admitted of a consider- 

 able reduction of species, but I fear I may thereby have 

 committed mistakes. The investigation of the species is the 

 more difficult, as the types are not labelled according to the 

 Illustrations but accordinsf to the Cataloo;ue, and some of 

 them do not agree with the descriptions. 



Westwood in his Introduction gives a masterly sketch of 

 the families and their habits. In the Synopsis he enu- 

 merates fifty-six species, namely, 6 Ephemera, 10 Lepto- 

 phlebia (^Potamanthus), 23 Baetu, 5 Brachycerus, 2 CcBtiis, 

 10 Clo'eon. Walker in the British Museum Catalogue de- 

 scribes no new English species. 



In working out this synopsis I have carefully compared 

 the species in my collection with the existing descriptions, 

 and have arrived at the conviction that our knowledge (or 

 at any rate mine) of the Ephemeridce is still very defective. 

 Instead of the fifty-six species hitherto recorded as British, 

 I can only make out the trifling number of twenty-five. 

 I am sure that England possesses a considerably greater 

 number of species, and probably on a more careful investi- 

 gation of the types some of my reductions would be found 

 to be incorrect. My work only represents the state of my 

 knowledge of this remarkable family. I have, however, 

 endeavoured to avoid errors as far as possible, and have 

 therefore, when practicable, always made the descriptions 



